Lung cancer is one of the most common cancers worldwide. It consists of two different subtypes: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Despite novel therapeutic options such as immunotherapy, only 20% of lung cancer patients survive the disease after five years. This low survival rate is due to acquired drug resistance and severe off-target effects caused by currently used therapies. Identification and development of novel and targeted therapeutic approaches are urgently required to improve the standard of care for lung cancer patients. Here, we describe the recent development of novel drug-delivery approaches, such as adenovirus, lipid nanoparticles, and PROTACs, that have been tested in clinical trials and experimentally in the context of fundamental research. These different options show that it is now possible to target protein kinases, phosphatases, ubiquitin ligases, or protein modifications directly in lung cancer to block disease progression. Furthermore, the recent acceptance of RNA vaccines using lipid nanoparticles has further revealed therapeutic options that could be combined with chemo-/immunotherapies to improve current lung cancer therapies. This review aims to compare recent advances in the pharmaceutical research field for the development of technologies targeting post-translational modifications or protein modifiers involved in the tumorigenesis of lung cancer.  In this review, we describe novel therapeutic approaches that take advantage of protein modifications in lung cancer. Protein modifications include phosphorylation, or the addition of a phosphorylated residue on a serine, threonine, or tyrosine, and ubiquitination, addition of a ubiquitin molecule to a lysine residue. While ubiquitination is involved in protein degradation through the proteasome and trafficking to vesicles, phosphorylation is important for the (in)activation of proteins, especially in signaling cascades such as mitogen activated protein kinase (MAPK) signaling cascade that is involved in cancer cell proliferation and survival. Kinases and phosphatases are enzymes involved in the phosphorylation or removal of the phosphorylation from a protein cargo. Several phosphorylation cascades are important for tumorigenic transformation or progression and have been extensively characterized. Several therapeutic design options focusing on specific kinases or phosphatases dysregulated in lung cancer progression were developed in the past years with various levels of success. This is key for the field as kinases, phosphatases, or ligases affecting oncogenic signaling are often mutated or deleted in lung cancer.In the case of kinases and phosphatases, these therapeutic strategies involved adenoviral-based or lipid nanoparticle-based drug delivery approaches. In the case of ubiquitination, the E3 ubiquitin ligases and E2 ubiquitin conjugating enzymes are the proteins that define the ubiquitination reaction specificity and catalyze the ubiquitination, respectively. Several E3 ligases have been described to act as tumor suppressors or promoters, further linking this protein modification with oncogenesis. Recently of interest in the drug development field, taking advantage of the ubiquitin system, proteolysis targeting chimeras (PROTACs) were shown to be promising approaches in order to trigger the degradation of oncoproteins, while deubiquitinase targeting chimeras (DUBTACs) allowed the stabilization of onco-suppressors. PROTACs and DUBTACs are specific probes that recruit ubiquitin ligases, induce degradative ubiquitination, or ubiquitin hydrolases (de-ubiquitinases) that remove degradative ubiquitin chains from specific targets.These different innovative approaches show that it is now possible to target protein modifications directly to block tumor progression. Targeting tumor specific protein modifications could also reduce off-target effects of anticancer drugs and side effects. Other protein modifications occur frequently in cancer, such as oxidation, glycosylation, nitrosylation, or ISGylation. These modifications directly affect the function of oncoproteins and oncosuppressors but have not been characterized enough yet, making it impossible to design therapies targeting them yet.Adenoviruses, many of which are responsible for respiratory infections in humans, have been genetically engineered to allow the delivery of genetic material to cells. These viruses demonstrate the ability to target a various range of cell types, as it is possible to use different serotypes that have specific affinity to specific cell types. Adenoviruses have a strong affinity for lung epithelial cells, from which most lung cancers are driven. Adenoviral-based therapies are genetic therapies that enable the expression of a protein of interest at a high level without showing any DNA integration or immune response towards the recombinant adenovirus. The efficiency of such therapies has been demonstrated in several genetic diseases  and, more recently, by the use of adenoviral-based vaccines against COVID-19 respiratory diseases. Several clinical trials have tested with some degree of success adenovirus-based approaches to impair oncogenesis, based on specific cancer-specific genetic mutations such as the one affecting p53 function, as indicated by Recent studies indicate that the primary receptor of adenoviruses on the cell surface, Coxsackie-adenovirus receptor (CAR), is expressed at different levels in various types of tumors. This could result in resistance to adenovirus infection in some cancer types, indicating that the adenoviral approach could be suboptimal in some types of cancer. However, a recent publication showed that the Coxsackie-adenovirus receptor is expressed at a high level in non-small cell lung cancer , indicatFurthermore, several adenoviral-based clinical trials indicated above in 13 particles when compared to classical adenoviruses [Another point of interest is the delivery route, as it was shown that different administration routes for the adenovirus gene transfer vectors could present different levels of innate immune response. This was quantified in a clinical trial by measuring interleukin-6 levels (IL-6) . The besoviruses . These dKRAS (Kirsten rat sarcoma virus) or EGFR . Mutations of BRAF (B-Raf proto-oncogene) or ERBB2  occur in a smaller subset of patients. Some phosphatases or kinases associated with these pathways are mutated in up to 40% of lung cancer patients, further indicating the relevance of therapies targeting these modifiers of oncogenic signaling. Mutations of the kinases or phosphatases indicated in KRAS, confirming the rationale for the investigation of these as potential therapeutic targets.Non-invasive imaging, such as computer tomography (CT) scans, has been described as the best approach to assess the efficiency of adenoviral-based gene therapy in lung adenocarcinoma, as indicated by a clinical trial in 1999 . PositroBRAF activating mutation. PI3K is essential for oncogenic signal transduction as it directly regulates downstream effectors important for transcription or metabolic deregulation. This indicates that re-activating this kinase using adenovirus-based therapy could be used to treat this type of cancer in combination with classical drugs used in lung cancer presenting BRAF mutations, such as BRAF or MEK inhibitors, dabrafenib, or trametinib. This could also uncover therapeutic options involving kinases that are commonly inactivated in cancer cells for lung cancer patients who are resistant to such therapies , a phosphatase that regulates the downstream functions of KRAS. One recent study identified PP2A as a key modulator of resistance to MEK inhibition in KRAS mutant lung cancer, across a library of more than 200 kinase inhibitors. This indicates that anti-PP2A therapy could be a valid option for drug-resistant lung cancer. Furthermore, it was recently shown that KRAS G12D-induced lung tumorigenesis was significantly accelerated in Ppp2r4 gene-trapped mice as compared to Ppp2r4 wild-type . This evThe phosphatase tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) also appears to have strong therapeutic potential for targeting through viral-based approaches in vivo. PTEN is a negative regulator of the phosphoinositide 3-kinase/AKT survival pathway, that exhibits strong tumor-suppressive activities, as the PI3K/AKT signaling pathways are activated by KRAS and EGFR mutations. Combined adenovirus-mediated PTEN (AdVPTEN) gene therapy with DNA-damaging anticancer drug cisplatin chemotherapy, appeared to dramatically reduce the progression of a murine model of lung cancer, due to induction of growth arrest and apoptosis in tumor cells. This shows that adenoviral delivery of PTEN could restore sensitivity to cisplatin in resistant lung cancers, further strengthening the hope for novel adenoviral therapies in cancer. These three examples demonstrate the potential for adenoviral-based therapies in the targeting of kinases or phosphatases specifically dysregulated in lung cancer, as this could reduce off-target effects and enable the design of better combinational therapies for patients with lung cancer.Degradation of targeted proteins using proteolysis targeting chimeras (PROTACs) has recently gained a lot of momentum. A PROTAC is a bifunctional molecule that consists of different parts: a ligand that interacts with the protein to be degraded and another ligand that binds to an E3 ubiquitin ligase to promote the degradation of a specific target. The efficacy of PROTACs has been shown to be hard to predict, especially in the context of cancer. A recent article indicated that the design of the PROTACs should be optimized for each type of cancer , as the KRAS G12C oncogenic mutation being the most frequent lung cancer driver. A recent study targeted KRAS G12C specifically in lung cancer, using a PROTAC that engaged Cereblon (CRBN). The PROTAC interacted with KRAS G12C in vitro, induced dimerization with CRBN, and degraded GFP-KRAS G12C in cells when overexpressed, but failed to degrade endogenous KRAS G12C in lung cancer cells [KRAS-G12C mutations are the most common, other residues are often mutated, causing cancer, such as G12D, G12V, or Q61N. These different mutations should also be targeted to propose therapies for patients presenting these different mutations, making it a challenge as it would be essential to propose targeted therapies for each type of genetic alteration affecting KRAS.Kirsten rat sarcoma virus (KRAS) mutations are responsible for up to 30% of lung cancer cases, with the er cells . This daer cells . While tAnother regulator of oncogenic progression in lung cancer is son of sevenless homolog 1 (SOS1). Targeting SOS1 is of strong interest because such an approach could be used in patients with different oncogenic KRAS mutations, regardless of the residue where the mutation occurs. SOS1 is a guanine nucleotide exchange factor (GEF) that acts as a downstream regulator of KRAS signaling, for which novel inhibitors were recently developed for combination anti-cancer therapies . SOS1 isKRAS or BRAF mutations, as these alterations are known to activate the FAK signaling cascade on top of the classical MAPK cascade involving MEK1/2.Focal adhesion kinase (FAK) was also described as a promising therapeutic target for KRAS-mutant lung cancer. However, clinical trials testing FAK inhibitors only showed limited antitumor activity . Recent Another commonly mutated genetic driver in lung cancer is the epidermal growth factor receptor (EGFR), which is mutated in up to 25% of lung cancer patients. The standard of care for patients with EGFR mutations is targeted therapy with tyrosine kinase inhibitors (TKIs), but these treatments can lead to drug resistance. More than half of the drug resistance due to the EGFR TKIs was caused by an acquired T790M mutation in the kinase domain of the EGFR protein. Recent studies have described PROTACs designs that target a specific EGFR mutation using a Cereblon (CRBN)-based approach . The PROFinally, as an alternative, a novel technology has recently emerged to target ubiquitin hydrolases . DUBTACs are heterobifunctional molecules consisting of a protein-targeting ligand linked to a DUB recruiter via a linker a. DUBTACDelivery of an active drug or gene therapy to target tumor growth has been successfully achieved through specific structures, called lipid nanoparticles (LNPs), engineered to preserve the active components’ function while reducing side effects. The first attempt at cancer immunotherapies in 1995 was based on mRNA delivery via LNPs, when injection of mRNA encoding carcinoembryonic antigens elicited antigen-specific immune responses in mice. Following the wide acceptance of lipid nanoparticle-based anti-COVID-19 (Coronavirus Disease 19) vaccines , a numbeFor instance, lipid nanoparticles encasing mRNA encoding for Polo-like kinase1 (PLK1), kinesin spindle protein (KSP), and centromeric protein E (CENPE) have been recently described . TargetiBeyond LNP or AAV delivery of oligonucleotides, other strategies have proved successful. Systemic administration of the antisense oligonucleotide (ASO) targeting BCL2, augmerosen, downregulated the target BCL2 protein in metastatic cancer and, combined with standard anticancer therapy, helped resensitize patients with resistant melanoma . SimilarIn conclusion, we describe several therapeutic approaches that focus on protein modifications that are dysregulated in the progression of lung or epithelial derived cancer. Protein modifications include phosphorylation, or the addition of a phosphorylated residue to a substrate, and ubiquitination, the addition of a ubiquitin molecule that induces targeting to the proteasome of the vesicular system. While ubiquitination is involved in protein degradation through the proteasome and trafficking to vesicles, phosphorylation is important for the (in)activation of proteins, especially in signaling cascades such as the mitogen activated protein kinase (MAPK) signaling cascade that is involved in cancer cell proliferation and survival. Kinases and phosphatases are enzymes involved in the phosphorylation or removal of the phosphate molecule(S) from a cargo, respectively. Several therapeutic design options focusing on specific kinases or phosphatases dysregulated in lung cancer progression were developed in the past years with various levels of success. These therapeutic designs included adenoviral-based or lipid nanoparticle-based strategies, showing good bioavailability and tolerance in patients. Another approach exploiting the ubiquitin framework is the PROTACs or DUBTACs strategy, which also showed proper response in patients, after optimization of the delivery of the compound, which was the most limiting factor in that case.Our comprehensive integration of clinical trials and recent findings in fundamental research in the field properly demonstrates the strong interest for these novel pharmaceutical strategies. While the adenoviral-based therapies are the oldest and most tested ones, they appear to be less well tolerated when compared to mRNA-based lipid nanoparticle delivery systems, according to the different clinical trials. The mRNA-based lipid nanoparticle drugs showed fewer side effects in the different trials and are now widely accepted after the massive use of mRNA vaccines for COVID-19. This explains a shift towards lipid nanoparticles recently. However, adenoviral-based approaches can still be optimized through genetic engineering, such as the use of targeted promoters for cell-specific expression. While genetic targeting using adenoviruses or lipid nanoparticles is precise, modulating specific protein modifications occurring specifically in cancer cells could be even better tolerated. PROTACs are one of the key technologies for the degradation of oncoproteins and show tremendous potential. However, this technology is still much less advanced when compared to lipid nanoparticle-based mRNA delivery or adenovirus based therapy, as indicated by the comparatively small number of clinical trials ongoing with this technology .


We describe 3 patients in California, USA, with trichodysplasia spinulosa polyomavirus (TSPyV) infection of endothelium after steroid administration. We detected TSPyV RNA in tissue specimens by in situ hybridization, which revealed localization to endothelial cells. These cases suggest that diseases associated with endothelial inflammation could be associated with TSPyV infection. One case of cutaneous trichodysplasia spinulosa was used as a positive control for TSPyV RNA. We used the RNAscope 2.5 LS Probe-Hs-PPIB-sense probe (Advanced Cell Diagnostics), which is specific for peptidylprolyl isomerase B, to demonstrate the presence of intact RNA in the tissue sections. For negative in situ hybridization controls, we used tissue specimens from patients with Merkel cell polyomavirus-positive Merkel cell carcinoma and BK polyomavirus nephropathy and a T-cell lymphoma tissue microarray that included 1 case of Merkel cell polyomavirus-positive T-cell lymphoma.This case study was part of a larger project approved by the Stanford Institutional Review Board  designed to explore oncogenesis by alphapolyomaviruses. We identified rare cases on our next generation sequencing panel of solid tumors with off-target, high quality reads that aligned to the TSPyV genome. We hypothesized that some of these cases might represent TSPyV-mediated neoplasms. Our cases comprised 1 patient with metastatic lung adenocarcinoma involving the brain (case 1), 1 patient with meningioma (case 2), and 1 patient with a metastatic perivascular epithelial cell tumor involving the liver . It is uIn contrast to our hypothesis, we found that TSPyV RNA did not localize to neoplastic cells. However, TSPyV RNA localized to the endothelium in all 3 cases . The BK TSPyV is a DNA virus, and detection of TSPyV RNA indicates active viral replication and infection. Our in situ hybridization results suggest that TSPyV can infect endothelial cells, likely within various tissues. These cases provide insight into a potential cellular reservoir for TSPyV infection. In addition, these data raise the possibility that other diseases associated with endothelial inflammation could be associated with TSPyV infection. Overall, this small case series improves our knowledge of the scope of human TSPyV infection.


The authors further provide a brief overview on the therapeutic interventions that are currently pursued in the clinic to utilize Treg depletion or promotion strategies in the context of cancer immunotherapy and tissue-specific inflammatory and autoimmune diseases. In order to exert their tissue-specific effects, Treg cells utilize a variety of tissue homing and retention strategies by which they migrate to peripheral tissue sites, respond to microenvironment specific survival signals, and exert tissue protective functions. Brull et al. covers this aspect and discuss tissue-specific adaptation strategies that shape up cellular crosstalk between Treg cells and immune and non-immune cell types, both in the context of barrier tissue environment as well as immune privileged sites like CNS.Two review articles by Kraj discusses how Bone Morphogenetic Protein (BMP) signaling might contribute to this epigenetic reprograming through BMP receptor BMPR1a signaling, as deletion of BMPR1a in mature Treg cells leads to increasingly more peripheral Treg cells with lower levels of Foxp3 and a naïve phenotype, including reduced suppressive function. Besides mediators of plasticity and adaptation, striking changes in Kdm6b demethylase and Cdkn1 cell cycle inhibitor were observed, suggesting a dysregulated epigenetic reprogramming.Epigenetic reprogramming is key in establishing and maintaining Treg cell function, and likely a main player in generating their diversity. Yang discuss recent progress in our understanding of Treg metabolism in the context of tissue homeostasis and functions, and its implications on defining Treg-mediated and Treg-aiming novel therapeutic strategies against autoimmunity and cancer. In another review article, Lu et al. focus on downstream effector mechanism of metabolic reprogramming and metabolite mediated epigenetic modifications in Treg cells and its implications on Treg activation, differentiation and function.Over the last decade, immunometabolism has evolved as a crucial area of research interconnecting the changes in metabolism to the quantity and quality of immune response. Not surprisingly, distinct metabolic adaptation strategies are also utilized by Treg cells in non-lymphoid environments and at tumor sites to ensure survival, hemostasis and tissue specific functions. The article by Weiß et al. summarize recent advances on our understanding of Treg-mediated MI repair, made possible by the use of T cell receptor (TCR) transgenic mouse models with defined antigen specificity against the cardiac-specific part of the myosin heavy alpha chain MYHCA antigen  as well as parenchymal  origin.Heart failure is a worldwide problem with high rates of hospitalization and mortality. Two review articles provide comprehensive summary on the function and significance of Treg cells in myocardial infarction and conditions of chronic heart failure. Myocardial infarction (MI) involves a rapid inflammatory response followed by replacement of dead myocardium with fibrous tissue. Recent studies have shown that Treg cells directly promote proliferation and survival of cardiomyocytes in MI mice by producing CST7, TNFSFL1, IL33, FGL2, MATN2, and IGF2  model. IL-33 administration after TBI significantly reduced brain lesion size and improved neurological function, and importantly, Treg cell depletion significantly reduced the protective effect of IL-33 after TBI. Thus IL-33 and Treg cells may represent a novel immunotherapeutic strategy to improve TBI outcome. In another original research article, Yamamoto et al. made a challenging trial to create brain Treg cells in vitro. They co-cultured spleen-derived Treg cells with primary astrocytes or microglia to mimic the brain environment in the presence of various cytokines and growth factors. The results showed that the addition of IL-2, IL-33, and histamine to the astrocyte co-culture partially conferred characteristics similar to the brain Treg cell population. Brain Treg-like cells generated in vitro showed increased brain infiltration and improved pathology in stroke and Parkinson’s disease models compared with splenic Treg cells.Three articles of the Research Topic discuss Treg cells in the brain. Treg cells are abundant in the gastrointestinal tract, where microbiota induced pTreg and Treg cells of thymic origin, tTreg cells, coexist . The gasl repair . IL-33 aHajam et al. discuss the current progress in our understanding on recently discovered non-canonical unconventional functions of skin Treg cells. A different aspect of Treg-mediated unconventional functions is elaborated in recent years by using zebra fish as a model system, where Treg like (zTreg) cells have been identified, and their spectacular regenerative properties have been demonstrated in multiple organs  modulate Treg cell surface molecules, cytokine production and transcriptional regulators. Moreover, they describe the potential of current immunomodulatory therapies and give examples of how their anti-tumor effects might relate to targeting different functions of the intratumoral Treg cell compartment. Sekiya presents the role of the nuclear orphan receptor family Nr4a in the differentiation and maintenance of thymic Treg cells, and the nuances in Nr4a1 and 2 function, that seem to be heightened by signals from the tumor microenvironment. Within solid tumors, colorectal cancer (CRC) presents a quite unique situation, due in part to the large environmental interface that hosts most our commensal microorganisms. CRC has been characterized by a high frequency of TH17-like Treg cells, with an increased capacity to suppress T cell proliferation via their reduced expression of Tcf-1, yet increased pro-inflammatory function that drives polyp growth. As a consequence, there are contradictory observations regarding Treg cell correlation with outcome. Aristin-Revilla et al. dive deep into the heterogeneity of intestinal Treg cell populations, factors that contribute to generate it, and how this might explain the paradox regarding infiltration of Treg cells and prognosis in colorectal cancer. Importantly, they describe current therapeutic efforts designed to target molecules important for CRC tumor-infiltrating Treg cells and how they are faring in clinical trials.As critical enforcers of peripheral tolerance, Treg cells contribute to cancer establishment and progression . Treg ceMuralidhara et al. draws parallels between uterine and tumor Treg cells, and highlights the differences driven by the dynamic nature of the inflammatory environment and the mix-nature of foreign antigens. These issues are critical when considering treating cancer with anti-Treg cell therapies during pregnancy.Pregnancy represents a complex physiological situation in which a foreign tissue is growing within another living organism. This semi-allogeneic scenario evokes tumor immunity, and Treg cells play similar roles inducing a tolerogenic environment in which these semi-foreign, invasive tissues continue to grow. We edited this Research Topic to highlight and update readers on Treg cell phenotypic diversity and role in physiological functions beyond peripheral tolerance. We hope the audience benefits from recent discoveries and contributes to expand our knowledge of this growing field.All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.


Cl III malocclusion with a significant skeletal component presents a therapeutic challenge during adolescence. This article presents the encouraging results of an individualized two-stage treatment approach adopted for successful nonsurgical correction of severe skeletal Cl III malocclusion in an adolescent girl after the onset of puberty. An orthopedic approach involving simultaneous alternate rapid maxillary expansion and constriction (Alt-RAMEC) protocol and protraction facemask (PFM) therapy was adopted in phase 1 to correct the sagittal skeletal discrepancy. In phase 2, fixed orthodontic therapy aided by the interim use of a modified occlusal settling appliance was undertaken to obtain well-interdigitated occlusion. Meticulously planned and well-executed orthopedic and orthodontic approach, combined with good patient compliance and favorable growth pattern, helped establish well-balanced facial harmony with a proper maxillomandibular relationship and satisfactory overjet and overbite. The results remained stable during the 4-year follow-up. Alt-RAMEC-PFM therapy accompanied by fixed mechanotherapy is a viable option to treat severe skeletal Cl III malocclusion in adolescents. Since late mandibular growth tends to worsen the Cl III discrepancy,2optimizing treatment timing is crucial for ensuring successful management as treatment difficulty increases considerably over time. During growth, maxillary deficiency has been documented to be a significant etiologic component3;it has also been reported to be a key determinant for good prognosis.5 CI III malocclusion, although less prevalent than Cl I and Cl II malocclusion,8More recently, early treatment with Liou’s9 alternate RME and constriction (Alt-RAMEC) protocol has been demonstrated to enhance subsequent sagittal maxillary protraction, albeit on a short-term basis.10However, there is limited literature on the long-term positive response to concurrent Alt-RAMEC and PFM therapy to correct severe skeletal Cl III malocclusion in adolescents to the best of our knowledge. Rapid maxillary expansion (RME) accompanied by protraction facemask (PFM) therapy is a popular modality for early correction of skeletal Cl III malocclusion during the deciduous and mixed dentition periods. This article reports the effectiveness of an individualized orthopedic‒orthodontic approach adopted for successful treatment of an adolescent girl with severe skeletal Cl III malocclusion. The treatment involved concurrent Alt-RAMEC and PFM therapy as the initial first stage orthopedic procedure, accompanied by comprehensive fixed mechanotherapy performed during the second stage. The stability of the clinically acceptable aesthetic and functional outcomes are also discussed. A 12-year-old girl presented, complaining of prominent lower front teeth, protruded chin, and compromised mastication and phonation. She had very low self-esteem as she was constantly ridiculed for her unpleasant smile and facial appearance. The family history was not suggestive of any genetic predisposition. Extraoral examination revealed a bilaterally symmetrical face, a mesoprosopic facial form, a concave facial profile with midface deficiency, a retrusive upper lip, a prominent lower lip, an acute nasolabial angle, and a shallow mentolabial sulcus . A low l Intraorally, she displayed bilateral Cl III molar and canine relationships with retained upper right deciduous canine and lower deciduous second molars. A long span of crossbite extending from the maxillary right deciduous canine to the left permanent first molar was observed. Incisor overbite was 5 mm, and overjet was -4 mm. The upper dental midline was shifted to the right of the facial midline by 2 mm. The lower dental midline was shifted to the left by 3mm compared to the upper dental midline . Both de A panoramic radiograph, taken at the early permanent dentition stage of development, did not reveal any bony or periodontal abnormalities . Cephalo Based on the clinical and cephalometric examinations, the cause of this patient’s malocclusion was an underdeveloped maxilla and mandibular prognathism. The treatment goals were to (1) improve the skeletal jaw relationship by protracting the maxilla anteriorly relative to the cranium and redirecting mandibular growth, (2) correct anterior and posterior crossbites, (3) eliminate CO/CR discrepancy, (4) achieve esthetically favorable and functionally effective overjet and overbite, (5) establish canine-guided functional occlusion with anterior guidance, (6) improve frontal and profile esthetics, and (7) ensure that the patient breathed mostly through the nose. Considering the patient’s age and severity of the skeletal and occlusal disharmony, a bone-anchored maxillary protraction treatment protocol was suggested since it offers the advantages of ensuring 24-hour bone-borne force, at the same time avoiding the problems associated with dental anchorage. However, the patient and her parents declined this approach because of the underlying concerns about the associated surgical risks. Thus, a conservative two-stage treatment approach commensurate with the patient’s young age and the parents’ wishes was adopted. An orthopedic approach involving concurrent Alt-RAMEC and PFM therapy for effective maxillary advancement was contemplated as a stage 1 procedure, followed by fixed orthodontic mechanotherapy during phase 2 to achieve well-interdigitated buccal occlusion. However, the parents were informed of the possible need for orthognathic surgery in the future, considering the likelihood of intermaxillary sagittal relationship worsening if the craniofacial growth proved unfavorable or if the patient did not comply with the recommended duration of orthopedic treatment. The first phase of treatment involved the Alt-RAMEC protocol performed with an 11-mm bonded Hyrax-type expander , with the simultaneous use of a Petit-type facemask for protraction of the maxilla. A 7-week Alt-RAMEC protocol of alternating expansions and constrictions commenced with expansion in the first week, alternating to constriction in the second week, and completed with expansion in the seventh week , and 3c.11consisting of retentive pin-head clasps and lateral acrylic flanges, was used as an interim adjunct to prevent lateral tongue thrust to facilitate rapid settling of buccal segment occlusion  was observed . At the cclusion . Third molar germectomy was performed, followed by distalization of the mandibular right second molar, using compressed nickel-titanium open-coil spring on a 0.017*0.025-inch stainless steel (SS) wire to create space for mandibular right second premolar. Simultaneous use of short Cl III elastics helped counteract the mesial reactionary forces. Once adequate space had been created, the second premolar erupted spontaneously in its position in the arch . A norma While maintaining the original intercanine width in mandibular arch form, individualized first- and third-order bends were carefully incorporated in the maxillary and mandibular continuous 0.019*0.025-inch SS archwires to detail the tooth positions. Judicious use of short and light (3.5 oz.) Cl III and vertical spaghetti elastics helped improve occlusal interdigitation. After debonding, retention consisted of maxillary and mandibular wraparound Hawley retainers worn during the daytime and a reverse twin block (RTB) appliance at night for 24 months. The patient was regularly monitored every six months to evaluate mandibular growth. The total treatment duration was 27 months. Post-treatment final records showed the achievement of the desired treatment objectives, i.e., significant improvement in facial esthetics with the correction of the maxillary deficiency, better lip support and an improved nasolabial angle, along with the establishment of normal overjet and overbite, and well-intercuspated buccal occlusion with canine guidance . Dramati A panoramic radiograph revealed good root parallelism with no significant apical resorption . Cephalo At 2.5-year and 4-year follow-up appointments, the harmonious facial balance and intermaxillary dental relationships were well-maintained  and 9.12With CVMI indicating 25%-45% of the remaining skeletal growth, and considering the small window of nonsurgical therapeutic opportunity due to the possibility of heavy interdigitation of the circummaxillary sutures around puberty,13it was decided to perform PFM therapy simultaneously with the Alt-RAMEC procedure, rather than waiting until the completion of the Alt-RAMEC protocol. This modification was under the recommendations of Canturk and Celikoglu,14 who demonstrated similar positive outcomes with this modified orthopedic protocol. Treating severe skeletal Cl III malocclusion during adolescence is challenging, especially when a conservative approach is adopted. It is imperative that the selected treatment plan reflect optimal treatment timing and prognosis of growth by evaluating skeletal maturity.15 norm of 31 mm. This facilitated effective and pronounced reciprocal disarticulation of both the sagittal and coronally running circummaxillary sutures, without consequent over-expansion, augmenting the skeletal effects of maxillary protraction.17 Alt-RAMEC was adopted as the procedure of choice instead of RME since our patient exhibited no pure transverse maxillary deficiency with an intermolar distance of 33 mm, which was higher than McNamara’s17 Therefore, to avoid the impending possibility of the risk of creating a jiggling effect in recurring weeks with the 9-week Alt-RAMEC when employed in permanent dentition,18a 7-week protocol was selected for our patient. Moreover, the implementation of at least 7-week Alt-RAMEC facilitates the greater quantitative opening of the coronally running circummaxillary sutures needed for more effective maxillary protraction than the 5-week protocol that does not elicit adequate opening of coronally running sutures.17More recently, it has also been reported that reduced buccal alveolar bone thickness of the expander’s anchor teeth observed immediately after the 7-week Alt-RAMEC protocol is within the scope of the initial alveolar thickness of the expander’s anchor teeth.19With judicious application of alternating rapid expansion/constriction course at a rate of 0.4‒0.5-mm activation per day instead of 0.8‒1 mm per day, no deleterious post-expansion effects were observed concerning root or bony dehiscence or compromised periodontal support of the anchor teeth, and the patient well tolerated the entire treatment process. Different weekly sequences of Alt-RAMEC protocol varying from 4 to 9 weeks have been proposed in the literature. However, there is no clear consensus about which weekly sequence should be employed. Similar effects have been reported with nine weeks and seven weeks of Alt-RAMEC for the subsequent maxillary protraction.20 significantly contributed to improvements in maxillomandibular and intermaxillary dental relationships, respectively, with the restoration of profile esthetics in our patient. It has been widely reported that the effects of maxillary protraction are predominantly skeletal in younger children and mostly dentoalveolar after 10 years of age.21The clinically significant maxillary advancement observed after pubertal onset in our case could be attributed to the synergistic effects of combined Alt-RAMEC and PFM therapy, enabling enhancement of the orthopedic effects of a facemask by the Alt-RAMEC protocol, and vice versa. The downward displacement of the maxilla also helped optimize the patient’s lip line and improved upper incisor exposure. Since the patient had a hypodivergent growth pattern, mild clockwise mandibular rotation did not compromise our patient’s esthetics. Moreover, according to the findings of Celikoglu and Buyukcavus,22significant improvements in upper pharyngeal airway dimensions and insignificant changes in the lower pharyngeal dimensions were also discernible in our patient. The well-documented orthopedic effects  and orthodontic effects (proclination of the maxillary incisors and retroclination of the mandibular incisors) induced by maxillary protraction23It is noteworthy that second molar distalization following elective third molar germectomy provided adequate space for the spontaneous eruption of the mandibular right second premolar. Germectomy is a short and simple procedure involving the removal of a tooth that had formed one-third or less of its root. Considering the severity and magnitude of posterior open bite following facemask therapy, application of heavy intermaxillary elastic traction was not feasible for the posterior leveling of the occlusal plane. Hence, the interim use of a modified occlusal settling appliance was considered more appropriate for aiding the closure of open bite. Placement of third-order bends in 0.019*0.025-inch SS wire during the finishing stage helped prevent further excessive buccal flaring of maxillary incisor crowns and allowed labial bodily movement.24Even so, the application of a combination of simultaneous Alt-RAMEC protocol and PFM therapy, accompanied by fixed mechanotherapy, contributed to establishing well-interdigitated Cl I dental occlusion without the loss of dental units while restoring facial esthetics to acceptable harmonious levels. Based on Wits appraisal of -8mm , the severity of Cl III patient featured in the present study was labeled as the ‘yellow’ category.25However, since our patient underwent orthopedic treatment after the commencement of puberty, it cannot be denied that the stability could have been jeopardized due to any impending residual growth.7Long-term appraisal of the treatment outcomes showed that maxillary changes and alterations in the sagittal position of the mandible were well-maintained at the end of active craniofacial growth. Institution of early protraction treatment before 10 years of age contributes to adult stability in 73%‒75% of cases. Good patient compliance in using removable appliances (including retainers) proved crucial for ensuring the stability of treatment results. In aptly selected cases, a synergistic combination of concurrent Alt-RAMEC and PFM therapy, accompanied by comprehensive fixed mechanotherapy, can be a viable treatment modality to correct severe skeletal Cl III malocclusion after the onset of puberty. This minimally invasive treatment protocol met the patient’s esthetic expectations, thereby uplifting her self-esteem. The reasonably stable results observed four years after treatment completion indicate that individualized treatment planning, adherence to sound orthopedic and orthodontic biomechanical principles, favorable growth pattern, and ensuring absolute patient compliance all contribute to maintaining long-term results. All authors have made substantive contributions to this manuscript, and all have reviewed the final paper before its submission. None. This case report complies with CARE guidelines for case reports, and written informed consent was taken from the patient’s parents for photo release. The authors declare no conflict of interests in connection with this article.


Angiogenesis describes the formation of blood vessels from an existing vascular network. Anti-angiogenic drugs that target tumor blood vessels have become standard of care in many cancer entities. Though very promising results in preclinical evaluation, anti-angiogenic treatments fell short of expectations in clinical trials. Patients develop resistance over time or are primarily refractory to anti-angiogenic therapies similar to conventional chemotherapy. To further improve efficacy and outcome to these therapies, a deeper understanding of mechanisms that mediate resistance to anti-angiogenic therapies is needed. The field has done tremendous efforts to gain knowledge about how tumors engage tumor cell and microenvironmental mechanisms to do so. This review highlights the current state of knowledge with special focus on the metastatic tumor site and potential therapeutic relevance of this understanding from a translational and clinical perspective. Angiogenesis is a biological process that describes the formation of new blood vessels from an existing vascular network. It is essential in many physiological processes including embryonical development or the female reproductive system . It is fWhen a developing malignant lesion reaches a critical size, diffusion does not sufficiently cover the increased demand for nutrients and oxygen. The core of this lesion becomes hypoxic leading to the stabilization of HIF-1 alpha. This induces the upregulation of many target genes that foster tumor progression. Among them are several so-called pro-angiogenic genes that orchestrate the ‘angiogenic switch’ by which the tumor recruits blood vessels from the surrounding healthy tissues enabling exponential tumor growth , 3. BesiLong before tumor angiogenesis was viewed ‘officially’ as one central ‘hallmark of cancer’ that is crucial for tumor progression at the primary tumor site and metastatic dissemination –8, JudahCompared to initial prospects which based on very promising experimental basic research and preclinical data –16 as weIn parallel to the Hurwitz Trial researchers sought to find prove and insights in how VEGF blockade with bevacizumab exactly works to inhibit tumor growth and progression. It became clear that the main mode of action of pharmacological VEGF withdrawal is the correction of functional and structural tumor blood vessel abnormalities. This has been summarized by Jain under the term ‘vascular normalization’ .It became clear that not only different tumor cell derived pro-angiogenic growth factors contribute to resistance against VEGF blockade, but also tumor stromal cells crucially mediate the efficacy and response to VEGF targeted therapies.Preclinical evaluation studies in mice exploring the efficacy of anti-angiogenic therapies have mainly been performed in disease models that only partially mimic clinical cancer situations. Many experimental findings are based on subcutaneous tumor models that involve a large primary tumor at best with metastasis at a single organ site and often without metastasis. Clinical evaluation and application of anti-angiogenic therapy, beside very few indications, take place in stage IV situations, often as second- or third-line therapy. This altogether makes preclinical and clinical findings often difficult to compare. Still cancer patients for the most part die from disseminated metastatic disease and anti-angiogenic therapy is mostly used in this disease stage. It is therefore very likely that metastatic lesions and their tumor microenvironment significantly contribute to resistance to anti-angiogenic therapies. This review will give a focused overview over the current state of knowledge of mechanisms of resistance that is mediated by the tumor microenvironment with specific respect to the metastatic tumor site and its potential clinical implications.The simplest concept of resistance to VEGF inhibition is the compensatory upregulation of alternative pathways. Accordingly, several dual or multi-targeting approaches that involve mainly the angiopoietin-2 (ANG-2)/TIE2 axis, platelet derived growth factor receptor beta (PDGFR-beta) signaling and fibroblast growth factor receptor (FGFR) signaling –25 have Targeting or manipulating ANG-2/TIE2 signaling has been demonstrated to show beneficial effects on tumor vascularization, vascular normalization and prolonged survival in murine models of multimodal treatment strategies , 28 29)29). ClinTargeting both VEGF and ANG-2 had additive effects on tumor growth, vascularity and vascular normalization in preclinical models by various mechanisms , 23–25. One of the perennial questions also here remains how findings from preclinical models that focus on primary tumor growth can be translated into stage IV clinical diseases. One phenomenon highly relevant for systemic cancer disease that seems to be tightly connected to resistance to anti-VEGF therapy that can potentially overcome by ANG-2 inhibition or ANG-2/TIE2 manipulation is the recruitment of myeloid cells to primary tumors and metastatic lesions.Tumor-infiltrating myeloid cells constitute the majority of the cellular tumor stroma. They can hinder or foster tumor progression depending on the disease entity, stage and treatment modality, specifically in the context of anti-angiogenic treatment , 28–30. A broad spectrum of neutrophils, macrophages and myeloid-derived suppressor cells (MDSCs) characterized by positivity for CD11b and GR1 (Ly6G/C) have been found to be associated with refractoriness to anti-VEGF therapy in multiple murine tumor models . This waWhether targeting bone-marrow derived sources of resistance to anti-angiogenic therapy can be translated into the clinic warrants further careful investigation specifically in the context of metastasis.+ neutrophils predicted poor outcome to bevacizumab containing chemotherapy in patients with stage IV colorectal cancer  has been integrated into treatment regimens of many cancer entities . There ihaustion –51 wherehaustion , see alsAccordingly, based on many preclinical studies, combining IT and anti-angiogenic therapy has been suggested as a promising synergistic concept . Which p38,39.Tumors do not exclusively engage neoangiogenesis to recruit and hold a vascular system available. Tumor cells can also grow along existing vasculature of the diseased organ without inducing neoangiogenesis, a term called vessel co-option Accordingly, the main target for current clinically approved anti-angiogenic therapy is far less relevant as the vasculature is not dependent on VEGF.Vessels histologically proliferate less and exert an increased pericyte coverage as indicators for a mature, non-activated vascular systems. It is very important to notice that the simplest measure of tumor vascularity, the microvessel density, does not indicate which type of vascularization, angiogenesis or vessel co-option is present in a tumor Especially in metastatic lesions vessel co-option is a frequently observed characteristic of tumor progression and a long-suspected cause of resistance to anti-angiogenic therapy . The occFrentzas and colleagues were able to connect histopathological growth patterns of these metastases that involve vessel co-option to poor response to bevacizumab . They coThis work furthermore demonstrated that tumor cells require actin-related protein 2/3 complex (Arp2/3) to successfully perform vessel- co-option. Accordingly, knockdown of ARPC3 a subunit of Arp2/3 blocked cancer cell motility thereby inhibiting vessel co-option and re-sensitizing tumors to anti-angiogenic therapy containing cytostatic treatment .Summarizing, vessel co-option might be a major cause why anti-angiogenic treatment is ineffective for example in a large proportion of patients with CRC liver metastases.Future efforts should focus on two things: (i) to design clinical trials to prospectively prove that response to and outcome after bevacizumab containing chemotherapy depends on histopathological growth patterns involving vessel co-option, (ii) develop treatment strategies that inhibit both vessel co-option and neoangiogenesis, especially in the context of metastatic disease. Furthermore, it is highly relevant to further clarify the role of anti VEGF therapy with bevacizumab or other drugs in multi-modal treatment strategies. The notion that upfront surgery followed by chemotherapy plus bevacizumab improves patients overall survival compared to upfront surgery plus chemotherapy without bevacizumab in patients with metastatic colorectal cancer underscores how relevant this might be .Another challenge is to develop and clinically evaluate techniques that can pre-therapeutically define the histopathological growth pattern which could guide clinical treatment decisions, e.g. in individual multimodal treatment concepts involving chemotherapy +/- targeted therapy prior surgery  or vice versa .From a metabolic perspective (neo)-angiogenesis is a highly demanding cellular process. Endothelial cells (ECs) that under quiescent, steady state conditions line the inner surface of each blood vessel, maintain their cellular homeostasis under opulent conditions. They consume low amounts of energy while being exposed to the most comprehensive environment, the blood stream. When a growing malignant lesion secretes proangiogenic signaling molecules that activate endothelial cells this relation between supply and demand is completely shifted. The growing vessel, initially mainly constituted by the endothelial sprout, elongates towards a nutrient poor and hypoxic, acidic environment. To execute this challenging task, endothelial cells undergo a ‘metabolic’ switch that involves upregulation of key metabolic pathways. The knowledge of endothelial specific metabolic features is just beginning to be expanded, especially the specific role of tumor endothelial cells. From a clinical perspective endothelial cell metabolism offers many opportunities to explore novel therapeutic targets that might contribute to overcome resistance to growth factor targeted strategies.Glycolysis is until now the best characterized metabolic pathway in endothelial cells. Specifically, tumor endothelial cells upregulate their glucose metabolism by several mechanisms. This is noteworthy as tumor cells are also considered to use mainly ‘aerobic’ glycolysis as energy resource and to fuel side pathways. Among other things the following: i) tumor ECs upregulate the glucose transporter GLUT-1 , ii) tumin vitro and vivo. The fact that manipulation of the endothelial cell glycolytic metabolism was able to alter endothelial cell sprout differentiation showed the immense role of endothelial cell metabolism that might overrule even growth factor receptor signals  indeed play an important role in activated endothelial cells and are indeed functionate , 72.Manipulating endothelial cell mitochondrial metabolism has broad effects on endothelial cell integrity and function , 73–75. via the respiratory chain to generate ATP by oxidative phosphorylation . E.g. tumor associated macrophages (TAMs) can be manipulated towards a hyper-glycolytic metabolic phenotype thereby ‘steeling’ glucose from endothelial cells which results in vascular normalization, lowers hypoxia and decreases metastasis . Tumor dAnother aspect is how targeting tumor and stromal metabolism can influence efficacy of anti-angiogenic compounds. Navarro et al. could demonstrate that vascular normalization by anti-angiogenic therapy modulates tumor cell metabolism away from glycolysis towards OxPhos. This sensitized tumor cells to the mitochondrial inhibitor ME344. ME344 acted synergistically with several anti-angiogenic compounds among them regorafenib which showed resistance as a single-agent . A phaseAccumulating evidence suggests that dosing of anti-angiogenic therapy is more complex than previously thought, especially compared to intense multi-substance chemotherapy regimens. Dose escalation of bevacizumab from 5 mg/kg to 10 mg/kg in combination with fluorouracil and leucovorin failed to further improve survival and response to treatment compared to fluorouracil and leucovorin alone in patients with metastatic colorectal cancer. Furthermore, only the lower dose of bevacizumab showed a significant improvement in response rates not the high dose .Reasons for this clinical finding can be multifaceted. Besides biases from the study design and patient recruitment of this study a potential mechanism behind this is related to the window of normalization, in which structural and functional abnormalities of insufficient tumor vessels become corrected improving delivery of chemotherapy. This is dose and time-dependent and varies from tumor entity to entity and potentially from patient to patient making clinical application and patient selection even more complicated , 87. PrePrior to the introduction of novel anti-angiogenic treatments to clinical application, lessons learned regarding the importance of dosing of anti-angiogenic therapies should be considered.Another important question with high clinical relevance is how the (metastatic) tumor reacts on a therapy pause due to drug intolerance, scheduled drug holiday or prior surgery. In several murine tumor models, both murine orthotopic and subcutaneous models, intense VEGF withdrawal eliminates the endothelial compartment of a tumor blood vessel but spares vascular support structures, e.g. the basement membrane and pericytes , 82, 83.Besides of tumor cells and stromal cells solid tumors are composed of extracellular matrix (ECM).It was observed that VEGF blockade induces the deposition of extracellular matrix (ECM) consisting of collagen I and IV, hyaluronic acid and glycosaminoglycans. This is the case in both murine primary tumors, murine and human metastasis , 91. ConDesmoplastic stromal compositions are known to be associated with poor patient outcome e.g. in pancreatic cancer independent of anti-angiogenic therapy , it is tTo summarize, deposition of excessive amounts of extracellular matrix components as response to anti-VEGF therapy might represent a targetable mechanism of acquired resistance of the metastatic microenvironment which warrants further investigation.Primary tumors and metastasis are composed of tumor cells and stromal cells and a considerable amount of extracellular matrix (ECM). Structurally and functionally this tumor ECM composes basement membranes of mainly tumor blood vessels and the ECM of the interstitium . The latAnother very interesting aspect is the role of endothelial YAP (Yes-associated protein) and TAZ  which are important regulators of vascular development , 102 andAnti-angiogenic therapies have become part of many mostly palliative treatment regimens. After very successful preclinical work and promising first clinical trials 20 years ago, anti-angiogenic therapies failed to revolutionize anti-cancer therapies. Resistance appears after time similar to conventional cytostatic drugs. Tremendous efforts have been performed to uncover potential mechanisms of resistance to anti-angiogenic therapies. Though still nearly two decades after clinical approval of bevacizumab, targeting VEGF is the only broadly clinically applied antiangiogenic concept, not only in colorectal cancer.One major burden in the development of first-generation anti-angiogenic therapy was to disregard several initially already evident facts: (i) subcutaneous murine tumor models are very different to polytopic metastasized human cancers (ii) vessel co-option is insufficiently targetable with VEGF inhibition (iii) though VEGF is a very potent proangiogenic factor many other cytokines can drive angiogenesis instead (iv) the complex microenvironment(s) of polytopic metastasized cancer diseases exploits a plethora of mechanisms to foster tumor progression independent of VEGF.Accordingly, future studies should engage models that involve metastasis and test their hypothesis in  large human cohorts. The field has to balance a difficult bargain between two challenges: first, to bring novel strategies that apparently are more effective than ‘just’ inhibiting VEGF quickly to clinical application, among them combined VEGF and ANG-2 blockade or novel metabolism targeted strategies such as PFKFB3 inhibition; and second, to exclude as best as possible that these interventions produce detrimental unwanted modulations of the tumor and its microenvironment that exhaust the beneficial effects that were pronounced in preclinical studies. This has the potential to further improve patients’ outcome in colorectal cancer, brain cancer, ovarian cancer, esophagogastric cancer and many other entities .Additionally, serum biomarkers and radiologic tools, e.g. image guided determination of the vascular normalization windows  are urgeAll three authors conceptualized and wrote the paper. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Metastatic neuroendocrine tumour (NET) to brain has been reported in 1.5–5% of patients with NETs. Differentiation between intracranial NET metastasis and meningiomas can cause a diagnostic dilemma. We present a symptomatic case of a 66-year-old male with a history of left-sided skull base mass. The diagnosis of a meningioma was made based on the MRI findings and clinical presentation. The patient received radiation and the mass remained stable on serial MRI images at follow-up visits. Five years after his initial presentation, the patient’s mass showed further growth. He also complained of worsening of his recent diagnosis of irritable bowel syndrome and fluctuations in his blood pressure. Surgical resection was performed, and histopathological features were consistent with moderately differentiated neuroendocrine tumour. Further evaluation with 68 Gallium-DOTATATE positron emission-computed tomography (Ga-68 PET/CT) showed metastatic disease involving the bones, lymph nodes, and liver without convincing evidence of the location of primary malignancy within the bowel loops or the pancreas. The patient was started on combination of capecitabine and temozolomide with partial response and significant improvement of his symptoms. This case highlights the clinical and radiological behaviour of intracranial NET that can mimic the diagnosis of meningioma. NETs can rarely metastasize to the brain with an incidence less than 5% of patients.4 Since meningioma is the most common type of primary intracranial tumors,5 differentiating between a dural metastasis and a meningioma is crucial for patient management.The incidence of neuroendocrine tumors (NETs) has increased in the United States over the last two decades.Herein, we present a case of intracranial NET metastasis that mimics a meningioma in a patient without known history of NET at the time of diagnosis.A 66-year-old, right-handed male presented to the neurology clinic with intermittent paresthesia over the left cheek and chin region. In addition, he experienced an intermittent double vision that was worsening in the 3 months prior. Magnetic resonance imaging (MRI) of the brain showed an enhancing mass centered in the left cavernous sinus, with extension to the brainstem homolaterally, causing mild displacement of the medial left temporal lobe without evidence of brain oedema. The mass was infiltrating the left Meckel’s cave. The clinical and radiological findings were consistent with a meningioma .After multidisciplinary discussion, stereotactic radiotherapy was recommended over surgical resection given the location of the tumour with proximity to carotid artery and cranial nerves, making complete surgical resection a challenge. Therefore, the patient received a total of 5040 cGy of radiation over 28 fractions.During the 6-month follow-up, the patient had significant improvement of his diplopia and facial dysesthesias. Follow-up MRIs over the next 3 years showed stable appearance of the mass, and the patient showed complete clinical neurological recovery. However, almost 5.5 years after radiation therapy, a repeat MRI scan revealed significant enlargement of the prepontine and the cavernous sinus lesion with no associated neurological symptoms . On reviAfter multidisciplinary team discussion, the decision of partial surgical resection was recommended due to brain stem compression. The patient underwent resection of his prepontine mass that had caused brainstem compression with residual mass located at the cavernous sinus. He showed a reasonable post-operative recovery, although he had some difficulties such as persistent ataxia and syncope-like episodes. Surprisingly, the pathology came back as well-differentiated neuroendocrine tumour, with Ki 67 index of 10% and diffusely strong positive immunostaining for synaptophysin, chromogranin, and CDX2. The patient was referred to the neuroendocrine oncology clinic. 68 Gallium-DOTATATE positron emission-computed tomography (Ga-68 PET/CT) scan evaluation revealed metastatic lesions affecting liver, bones, and lymph nodes without evidence of primary tumour . The patThe patient’s mass continued to show response on CAPTEM with partial response in the liver lesions and stable MRI appearance and no evidence of new metastatic lesions. On the patient’s last visit , he denied any new seizures, headache, or cognitive dysfunction. He showed few symptoms of peripheral neuropathy without any neuropathic pain or subsequent falls. The patient is completely independent in all his daily living activities.6 Only 1.3–1.4% of all brain metastases have neuroendocrine tumour origin.7–9 Bronchopulmonary NET is the most frequent subtype to metastasize to the brain.In this report, we present a case of metastatic NET to the dura with radiological features suggestive of meningioma. The majority of NETs arise in the gastrointestinal tract or in the bronchopulmonary system. Most metastases occur in the liver, bones and, lungs, while intracranial metastases are extremely rare.10 Stereotactic biopsy should be recommended in cases that the tumours location allows any neurosurgical operation. Otherwise, repeat MRI imaging to show stability or slow growth over 6 months to a year or systemic imaging with CT or MRI to rule out metastatic disease may be helpful if the diagnosis of meningioma is in doubt. However, low-grade NET metastases may grow at a similar slow rate as is seen with meningiomas, thus in this rare case repeat MRI may have falsely generated confidence in the diagnosis of meningioma. Fludeoxyglucose (FDG) uptake on PET imaging is not useful, due to high physiological baseline uptake of the brain.11 However, FDG PET is a very useful modality for evaluation of metastatic disease in general.Dural metastases in general are not uncommon. Moreover, radiological features of many tumours including dural metastases on CT/MRI imaging are often similar to that of meningioma resulting in a diagnostic dilemma.12 This is because meningiomas routinely express somatostatin receptors and are universally positive on SRI.13 For this reason, SRI is known to be useful in distinguishing residual meningioma tumour from postoperative scarring in the post-operative setting.14,15 However, SRI can show moderate-to-high activity in a variety of tumour types that are somatostatin-receptor positive, such as NETs..16 Therefore, while SRIs might not distinguish NET from meningioma, the presence of extracranial somatostatin receptor positive lesions would point to a diagnosis other than meningioma.The national comprehensive cancer network guidelines recommend considering Somatostatin receptor imaging (SRI), such as octreotide planar and SPECT scans or 68 Gallium-DOTATATE PET scans if diagnostic doubt regarding the diagnosis of meningioma exists based on MRI features.17One of the radiotracers that may be, surprisingly, useful for differentiating meningiomas from other tumours is Pittsburgh compound B (11C-PiB) which is used in PET imaging in dementia. We have previously reported a 100% specificity for meningioma with (11C-PiB), although further research is required before this technique becomes part of clinical practice.18 Deshaies et al also reported a case of meningioma-like mass that turned out to be NET.19 In both our case and their case, carcinoid symptoms were present. This should maintain a high index of suspicion for NET in any patient with carcinoid like symptoms and an intracranial mass. Clinical suspicion should be raised in any intracranial mass including a dural-based lesion or a benign-looking mass that has undergone surveillance for several years. Imaging of NETs is often challenging and usually requires a combination of both anatomic and functional techniques.20 Metastasis of carcinoid tumour to intracranial meningioma is also a possibility and has been reported in the literature21Functional NETs secrete hormones that could result in variety of symptoms such as watery diarrhoea, labile blood pressure, and flushing, also known as carcinoid syndrome. The presence of such symptoms can help in the diagnosis of an indeterminate intracranial mass. However, there is often a long interval between the start of symptoms and diagnosis.22 Our patient’s last follow-up was around 8 years following his initial presentation with dural metastasis. Despite the relative short median survival time of patients with intracranial NET metastases, longer survival over five years has been reported in a few cases.22–24 This prolonged survival may be partially explained by the well-differentiated subtype of the tumours of those who lived longer22In our case, the positive CDX2 seen on pathology that is usually seen in gastrointestinal and pancreatobiliary tract tumours, raised the suspicion of the diagnosis of an intracranial metastasis of unknown origin. This concern was further raised when extensive systemic metastases were seen on imaging. Grade 1/2 NET patients with brain metastasis have an estimated median survival of 15 months from the time of brain metastases diagnosis.25,26 Our patient showed stabilised intracranial tumour and shrinkage of his liver metastases on his temozolomide and capecitabine treatment. Temozolomide can cross-blood brain barrier and it has shown a valuable effect in treating NETs either alone or in combination with capecitabine.6,27 This may highlight the clinical benefit of temozolomide in patients with brain metastases from NETs.22 Several factors should be taken into consideration in tailoring the treatment lines including patient age, neurological state, histological differentiation, tumour extension location of the tumour, and its relation to the surrounding structures . Further research may be needed in prioritising the different treatment lines.There is still no consensus regarding the standard treatment of intracranial NETs. Treatment options include surgical resection, somatostatin analogs including 177 Lutetium DOTATATE, whole-brain radiation or intensity-modulated radiation therapy. A prior study suggested comprehensive treatment including surgical resection and chemo-radiotherapy is expected to offer a longer tumour-free survival than surgical treatment alone.Intracranial NETs metastases are extremely rare. Carcinoid like symptoms and advanced imaging techniques could help in differentiating neuroendocrine metastases from meningioma. Multidisciplinary care should tailor a comprehensive treatment for patients with intracranial NETs for the best possible outcomes.Dural neuroendocrine tumour (NET) metastasis is extremely rare, and its differentiation from meningioma can cause a diagnostic dilemma.Clinical suspicion should include intracranial benign-looking mass; even that had undergone surveillance for several years, in patients with watery diarrhoea, flushing, or labile blood pressure symptoms.While Somatostatin receptor imaging might not distinguish NET from meningioma, the presence of extracranial somatostatin receptor positive lesions would point to a diagnosis other than meningioma. Pittsburgh compound B may play a promising role in the future.Multidisciplinary care should tailor a comprehensive treatment for patients with intracranial NETs for the best possible outcomes.