e11586 Background: We retrospectively analyzed efficacy of trastuzumab-based chemotherapy in patients whose disease progressed after lapatinib. Methods: Between October 2010 and May 2013, 54 patients whose disease progressed after lapatinib received trastuzumab-based treatment. Survival and toxicity results were evaluated retrospectively. Results: Median age of patients were 46 (27-67), 53 were female and 1 was male. 24 patients (44,4%) were ER-positive and 20 (37%) were PR-positive. 14 patients (25,9%) had metastasis at the time diagnosis. 36 of the patients (66,6%) had received adjuvant/neoadjuvant anthracycline and taxane therapy, while 24 (44,4%) had received adjuvant/neoadjuvant anthracycline and 14 (25,9%) adjuvant trastuzumab therapy. 47 patients had received trastuzumab in metastatic setting and all patients received lapatinib plus capecitabine. Median chemotherapy line for metastatic setting was 2 (1-7), 26 patients (48%) had received at least 3 lines of treatments. 39 patients (72,2%) had at lea...