Abstract P6-07-30: The clinical significance of pathologic complete response using different definitions after neoadjuvant chemotherapy in HER2 positive breast cancer patients according to hormonal receptor status.

Background: For patients (pts) with HER2 positive (HER2+) breast cancer, the achievement of pathological complete response (pCR) after neoadjuvant chemotherapy is regarded as a surrogate endpoint of prognosis, however, the exact definition of pCR and its prognostic impact on survival in HER2+ breast cancer subtypes when stratified by hormonal receptor (HR) status is uncertain. Methods: We retrospectively investigated 163 HER2+ pts who received neoadjuvant chemotherapy in Hyogo Cancer Center between 2003 and 2010. HR+ was defined as estrogen or progesterone receptor positive. pCR at surgery was defined as no evidence of invasive and noninvasive residual in the breast or axillary nodes (ypT0 ypN0), no evidence of invasive residual in the breast or axillary nodes; noninvasive breast residuals allowed (ypT0/is ypN0), or no evidence of invasive residual in the breast; noninvasive breast residuals and infiltrated lymph nodes allowed (ypT0/is ypN0/+). Logistic regression analysis and logrank test were performed to identify HR status as a predictor of pCR and its prognostic significance on recurrence-free survival (RFS). Results: The median age at diagnosis was 55 years (range, 25–84) and the median follow-up period was 61 months (range, 15–104). Stage I, IIA, IIB, III were 4, 57, 56, 46 pts, HER2+HR+ and HER2+HR- were 89 and 74 pts, respectively. The rates of pts receiving anthracycline, taxane and trastuzumab were 66, 82 and 51%, respectively. After surgery, 98% of HER2+HR+ pts received hormonal therapy. Five-year RFS rates were significantly higher in HER2+HR- pts with pCR compared to non-pCR, however, which were similar in HER2+HR+ pts with pCR compared to non-pCR regardless of the pCR definitions. In logistic regression analysis, significantly fewer HER2+HR+ pts achieved pCR compared to HER2+HR- pts regardless of the pCR definitions. Conclusions: HER2+HR+ breast cancer pts had lower achievement rate of pCR, which was less prognostic compared to that in HER2+HR- pts regardless of pCR definitions. pCR is a suitable surrogate end point for HER2+HR- pts but not for HER2+HR+ pts in clinical trial settings. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-07-30.