296PHER2-POSITIVE EARLY BREAST CANCER IN THE PRE-TRASTUZUMAB AND TRASTUZUMAB ERAS: A TRIPLE POSITIVE SUBGROUP ANALYSIS OF A MULTICENTER RETROSPECTIVE STUDY

ABSTRACT Aim: HER2-positive (HER2+) breast cancer (BC) is a heterogeneous disease, with a minority of patients presenting an excellent prognosis. Recent findings suggest that the efficacy of HER2-directed therapy may differ according to hormone receptor (HR) status, and this raised the question if HR status defines different subtypes of HER2+ BC. We conducted a multicenter analysis of HER2+ early BC patients to determine relapse free survival (RFS) and overall survival (OS), and to investigate the role of HR in outcome. Methods: We retrospectively enrolled HER2+ (IHC 3+ or 2+ amplified) early BC patients treated with adjuvant chemotherapy with or without trastuzumab (T) in 7 Italian oncologic centres until December 2011. A review of clinical and treatment data was carried out for analysis. Results: 769 chemotherapy-treated HER2+ early BC patients have been analysed and divided into two groups, T-untreated (N = 304, cohort A), and T-treated (N = 465, cohort B). Overall, the median follow-up was 68 months (range, 1-171). Three-year RFS for cohort A was 81.3%, whereas it was 92% for cohort B (p Conclusions: Although the benefit given by addition of T to adjuvant chemotherapy is clear in all subgroups analyzed, our data suggest the existence of a subset of TP BC, characterized by high levels of ER expression, that is driven both by HER2 and ER signalling, with a biological behaviour similar to ER-positive, HER2-negative BC. Disclosure: All authors have declared no conflicts of interest.