[Role of biological heterogeneity in recurrent and metastatic breast cancer].

Breast cancer (BC) is a heterogeneous tumor, the biological characteristics of which vary with its growth and progression. Information on key tumor receptors (ER, PR, HER2, and Ki-67) is the basis for individualizing the diagnostic and treatment algorithm at all BC stages; however, the feasibility of biopsy of distant metastases and the re-testing of the biological subtype of BC in its suspected progression are being actively discussed in clinical practice. This review presents an update on the features of metastasis in different biological BC subtypes and assesses the clinical and prognostic role of biopsy of distant metastases in the lung, bones, liver, and brain. It shows the frequency of discordance in receptor status between primary and recurrent tumors at different sites of metastases, as well as the impact of changes in receptor status on survival rates in different biological BC subtypes. The relevance of performing biopsies in BC progression is shown to be beyond question, because it makes it possible to confirm the fact that the disease progresses, to re-test the biological subtype of recurrent BC, and to find new targets that allow the most effective drug treatment regimens to be used.