Background: That tumor heterogeneity exists and evolves over time is well appreciated but how often to biopsy patients’ metastatic BC is not well established.
Methods: Immunohistochemical (IHC) and in situ hybridization (ISH) analysis of estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), and HER2 in 337 cases with >1 asynchronous primary/metastatic BC molecular profiles and in 40 cases with >1 synchronous molecular profiles was performed at a single institution.

We evaluated differences in ER, PR and HER2 status in same or contralateral breast, and in primary vs. locally recurrent or metastatic BC’s.