Predictive factors for pathologic complete response (pCR) to trastuzumab (T)-based neoadjuvant chemotherapy in HER2+ breast cancer (BC) women treated in the National Cancer Institute (NCI) of Mexico.

Abstract

634 Background: Neoadjuvant treatment identifies subgroups of patients (pts) with different prognosis. In HER2+ BC, some tumors have been reported to be more sensitive to anti-HER2 therapy than others. We conducted an exploratory analysis in HER2+ BC women who received T-based neoadjuvant chemotherapy. Methods: Clinico-pathologic data from HER2+ BC pts who received neoadjuvant chemotherapy and T between January 2007 and May 2012 at the NCI were identified. Estrogen receptor (ER), progesterone receptor (PR) and HER2 expression were determined by immunohistochemistry and/or FISH. pCR was defined as complete absence of invasive tumor in breast and axillary nodes. Proportion differences were tested using the Chi-square test. A generalized linear model was used for multivariate analysis. Results: 243 pts received T-based neoadjuvant chemotherapy for localized HER2+ BC tumors. Median age was 49 (26-72) years. 96% had positive axillary nodes at diagnosis and median tumor size was 5.5 (1.5-20) cm. 49.4% had hormone receptor (HR) + (ER+ and/or PR+) and 50.6% HR negative (ER- and PR-) tumors. 63.4% pts achieved pCR. HR negative tumors reached significantly higher pCR rates than HR + tumors (69.9% vs. 56.7%, p=0.034). Pts with inflammatory BC (n=27) had a trend to achieve pCR less frequently than the non-inflammatory tumors (48.1% vs. 65.3%). Those who received taxane-anthracyline sequence chemotherapy (n=20) achieved pCR in 70% of the cases vs. 62.8% with anthracycline-taxane sequence. Differences among other variables (age, tumor size, nodes and HER2 positivity ++/+++) were not significant. Variables that positively influenced pCR were HR negative status (p=0.015), non-inflammatory BC (p=0.082) and chemotherapy sequence (p=0.086). Conclusions: HR negative HER2+ BC tumors were associated with higher pCR, consistent with neoadjuvant trial reports. Preclinical data suggest bi-directional crosstalk between HER2 and ER pathways, which might influence anti-HER2 agents and chemotherapy sensitivity for tumors co-expressing both receptors. New strategies are needed to overcome resistance for HER2+ HR+ BC tumors.