298PEFFICACY OF ADJUVANT 9-WEEKS TRASTUZUMAB IN NODE-NEGATIVE T1A/B HER2-POSITIVE BREAST CANCER

Abstract Aim: The benefit of the addition of 9-weeks or 52-weeks adjuvant trastuzumab to chemotherapy compared with chemotherapy alone was shown in five randomized trials. Despite retrospective series having shown the poor prognosis of HER2-positive T1a/b node-negative tumors, the efficacy of adjuvant trastuzumab was not known exactly. The aim of this study is to evaluate the efficacy of trastuzumab in HER2-positive T1abN0M0 breast cancer. Methods: Newly diagnosed 705 T1a/b node-negative breast cancer patients from July 2000 to December 2013 in 13 clinics were retrospectively analyzed; a total of 166 HER2-positive patients were included in this study. In this study 54 (32.5%) patients were treated with adjuvant trastuzumab, whereas 112 (67.5%) patients were not treated with adjuvant trastuzumab. Demographic and medical data including age, performance status, tumor characteristics and comorbid diseases were collected from the medical charts. Kaplan–Meier survival analysis was carried out for DFS and OS. Results: The median age of the study population was 53 (24-79) years. Median follow up was 37 (2-157) months. Baseline demographic characteristics of both groups were similar and non-significant. In both treatment groups, median age, histology, menopausal status lymphovascular invasion and perineural invasion positivity were similar. But in trastuzumab treatment group grade 3 tumors were significantly higher compared with non-trastuzumab arm (55.1% vs 26.0%, P = 0.002). Also in trastuzumab treatment arm, combination chemotherapy (P < 0.001) were significantly used more than non-trastuzumab arm, whereas hormonal treatment (P = 0.002) were used significantly higher in non-trastuzumab arm. Median DFS and OS could not be obtained due to the low events in both groups. With a 37 months follow up, recurrence was observed only one patient (1.8%) in trastuzumab arm and 3 patients (3.6%) in non-trastuzumab arm. No exitus was observed during the follow-up period. Conclusions: In retrospective series, patients with HER2-positive T1abN0M0 tumors have a significant risk of relapse and recurrence. But in our study, due to the low events no comment can be made with 9-weeks adjuvant trastuzumab. Future studies with longer follow-up are needed to show the efficacy of adjuvant trastuzumab in HER2-positive T1abN0M0 breast cancer. Disclosure: All authors have declared no conflicts of interest.