[Hopes and pitfalls of the molecular classification of XXXX ].

@entity5 @entity0 @entity1722 @entity1491
Traditional histopathological diagnosis of @entity0 has been extended in recent years through the results of additional methods. Today, the results of the detection of hormone receptors, @entity1722 , and Ki67 antigen are thus an integral part of the histopathological diagnosis. A critical factor for the success of these tests is the fulfillment of pre-analytical phase conditions - i.e. optimal fixation, as well as taking into account the heterogeneous nature of the neoplastic population. In addition to the above-mentioned markers - which have become a routine practice in recent years, there are many efforts to include the molecular characteristics of @entity5 both in @entity5 classification as well as in the prediction of results of @entity5 treatment. Most of the work is based on the use of gene expression profiles. On the basis of the detection of increased or decreased expression of a large number of genes, it is possible to find a set of multiple genes correlating with the biological behavior of the @entity5 . Using this approach, four basic subgroups of @entity0 have been identified - luminal, basal-like, @entity1722 enriched and normal gland-like. Over the course of time, the number of molecular categories has expanded - originally a homogenous group of @entity5 has been subclassified into the luminal A, B and C. @entity1491 additional subgroups have been identified. However, the results of studies dealing with the analysis of gene expression profiles suggest that our understanding of the biology of @entity0 is far from being complete. The individual categories are defined differently in various publications and thus the comparison of the results of these studies is very difficult. Another approach for the molecular classification of @entity0 is the immunohistochemical detection of various proteins used as a surrogate marker instead of the detection of the mRNA of individual genes. The advantage of this approach is the possibility to use even archive material, as well as much lower costs. On the other hand, its main limitation is the inability of parallel detection of thousands of markers, unlike in genomic profiling. The results of molecular classification are, however, not fundamentally surprising. The fact that @entity0 stem cells can differentiate towards myoepithelial (or basal) and luminal cells has been known for a long time. These two lines of differentiation are - among others - characterized by differential expression of cytoskeletal proteins as well as of other molecules. These findings have been confirmed by the results of molecular studies - either those based on gene expression profiling or immunohistochemical ones. Research results in gene expression profiling have relatively quickly translated into clinical practice. At present, several commercially available certified tests serve as a complementary source of information for decisions about clinical treatment.
