The 21-gene recurrence score in special histologic subtypes of breast cancer with favorable prognosis.
BACKGROUND/PURPOSE
The 21-gene recurrence score (RS) assay predicts the likelihood of distant recurrence and chemotherapy benefit in early-stage, estrogen receptor (ER)-positive, HER2-negative breast cancer. Data on the RS of special histologic subtypes of invasive breast carcinoma with favorable prognosis are limited.


METHODS
We reviewed our institutional database to identify patients with special histologic subtypes of breast cancer associated with favorable prognosis and available RS results. Our cohort consists of fifty-seven women: thirty-three patients with pure mucinous carcinoma (MC), ten with tubular carcinoma (TC), nine with encapsulated papillary carcinoma (EPC), and five with solid papillary carcinoma (SPC).


RESULTS
Most (44/57, 77.2%) carcinomas had low RS (≤17), and none had high RS (≥31). All EPCs had low RS, but other subtypes had RS 18-30. Higher RS was associated with lower progesterone receptor (PR) expression by immunohistochemistry and lower PR mRNA scores (P ≤ 0.007). No morphologic feature (tumor grade, biopsy site changes, cellular stroma, inflammatory cells) was associated with RS ≥ 18. At a median follow-up of 40 months, the distant recurrence-free survival was 100%. One patient with SPC developed locoregional recurrence at 22 months.


CONCLUSIONS
As the largest series to date, our study raises the question of whether the RS assay is necessary for breast cancers with favorable histology. Reflex testing of node-negative, ER+/HER2- breast cancers may be deferred for these special histologic subtypes, emphasizing the need for multidisciplinary discussions between breast pathologists and other members of the breast cancer team.
['Turashvili|Gulisa|G|', 'Brogi|Edi|E|', 'Morrow|Monica|M|', 'Hudis|Clifford|C|', 'Dickler|Maura|M|', 'Norton|Larry|L|', 'Wen|Hannah Y|HY|']
D002288:Adenocarcinoma, Mucinous D000328:Adult D000368:Aged D000369:Aged, 80 and over D000970:Antineoplastic Agents D014408:Biomarkers, Tumor D001943:Breast Neoplasms D002291:Carcinoma, Papillary D016208:Databases, Factual D018572:Disease-Free Survival D005260:Female D020869:Gene Expression Profiling D020022:Genetic Predisposition to Disease D006801:Humans D008875:Middle Aged D009361:Neoplasm Invasiveness D009367:Neoplasm Staging D010641:Phenotype D057285:Precision Medicine D011237:Predictive Value of Tests D018719:Receptor, ErbB-2 D011960:Receptors, Estrogen D012307:Risk Factors D013997:Time Factors D059467:Transcriptome D016896:Treatment Outcome
Breast cancer Mucinous carcinoma Tubular carcinoma Encapsulated papillary carcinoma Solid papillary carcinoma Favorable histology 21-gene recurrence score assay