Impact of neoadjuvant HER2-directed therapy on HER2 status in breast cancer.

e12130Background: Neoadjuvant chemotherapy (NAC) with HER2-directed therapy has become standard-of-care for most women with potentially curable HER2-positive (HER2+) breast cancer and is associated with a high pathologic complete response (pCR) rate. The HER2 status of residual disease after NAC is not well characterized and could potentially inform clinical decisions about additional systemic therapy. We describe tumoral HER2 status before and after NAC with HER2-directed therapy. Methods: An institutional database was screened to identify patients with stage 1-3 HER2+ breast cancer by fluorescence in situ hybridization (FISH) and/or immunohistochemistry (IHC) who received NAC with HER2-directed therapy followed by resection between 2011 and 2015. Clinicopathologic data was collected. Change in HER2 status by FISH and IHC following treatment was described. Results: 99 patients were identified. Median age was 49 years (range 26-85). Pre-treatment median HER2/CEP17 copy number ratio (CNR) for all tumors wa...