150 Background: The systemic management of metastatic breast cancer (MBC) is mostly based on the ER or HER2 status of the primary tumor. However, the hormonal status or the amplificaction/overexpression HER2 may change in every metastatic site because of the effects of the long-term treatment of metastatic cancer with endocrine therapy, chemotherapy, or targeted agents. The purpose of this study was to investigate the frequency of change in HER2 expression in primary and distant metastatic tumors (especially in liver) in HER2+ breast cancer patients. Methods: We retrospectively analyzed the results of 31 consecutive metastatic breast cancer patients that were seen in our center over 4 months from February 2014 through May 2014. All patients were rebiopsied after consultation and samples were sent for standard immunohistochemistry (IHC) for ER, PR, and HER2 and formalin-fixed, paraffin-embedded (FFPE) samples were sent for genomic (Foundation Medicine) and proteomic analysis (Theranostics). All results from the metastatic samples were compared to the baseline IHC and/or FISH results for HER2. Results: A change in HER2 status was observed in 26% of the cases. 16% of cases underwent a negative to positive conversion in HER2 status while 10% of cases underwent a positive to negative conversion. It is notable that all 5 patients that underwent a negative to positive conversion in HER2 status had biopsies taken from metastatic disease in the liver. Overall, 45% of patients with metastatic disease in the liver had a negative to positive conversion in HER2 status. Conclusions: The results of this study emphasize the significance of confirming HER2 expression in a recurrence lesion. This discordance may be due to the increasing level of genetic instability occurring throughout disease progression that can significantly influence the alterations of the HER2 gene. If feasible, HER2 reassessment in metastatic lesions should be carefully taken into account, especially for metastases coming from non-HER2 amplified breast cancer. Although HER2 status is usually appraised in primary tumor, knowledge of the HER2 status in metastases may be of potential value for therapeutic decision making.
Clinical outcomes among HR+/HER2− metastatic breast cancer patients with multiple metastatic sites: a chart review study in the US