Rechallenge of Trastuzumab-based Therapy in HER2-Positive Breast Cancer Patients who Progressed Under TDM-1

Data on rechallenges of HER2 targetted agents in breast cancer patients is limited. The goal of the study was to evaluate the effectiveness of trastuzumab-based therapy in patients who progressed under trastuzumab emtansine (TDM-1). The study was designed as a retrospective observational study. Survival plots were performed with the Kaplan-Meier method. Fifteen patients were involved in the study. The average age was 45 (range, 30-66). De novo metastatic patient number was six (40%), and the average number of metastatic sites was 2 (range, 1-4) at diagnosis. Fourteen patients (92.3%) had undergone breast surgery (lumpectomy or mastectomy). All patients previously had been treated with trastuzumab-based chemotherapy and TDM-1. Also, nine (60%) patients had received endocrine therapy, and nine (60%) patients had palliative radiotherapy. After progression under TDM-1, patients received trastuzumab with chemotherapy (73.3%) or alone (26.7%). The overall response ratio was 66.7%. Median progression-free survival was 9.4 months (95% CI, 3.4-15.3). The median OS duration was 24.2 (95% CI, 13.5-34.9) months. Toxicity in all grades was observed in ten (66.7%) patients, and grade 3-4 toxicity (anemia and neutropenia) in two patients (13.3%). This study showed that rechallenge trastuzumab-based therapy was effective and good-tolerated in heavily pretreated patients who had progressed under TDM-1.