Abstract

Introduction: Trastuzumab emtansine (T-DM1) is currently approved for the treatment of patients with HER2-positive metastatic breast cancer after failure of prior anti-HER2 therapies. However, the efficacy of T-DM1 in patients who received pertuzumab, and in those patients with brain metastases, is currently unclear. Methods: A total of 63 women with HER2-positive metastatic breast cancer were treated with T-DM1 between April 2014 and April 2016. The efficacy and safety of T-DM1 therapy was investigated. Results: There were 43 (67%) patients with visceral metastases and 14 (22%) patients with brain metastases. As adjuvant or neoadjuvant therapy in 45 patients with recurrent breast cancer, 19 (30%) patients had received trastuzumab. In the metastatic setting, all but two patients (97%) had undergone trastuzumab, 41 (65%) patients had received pertuzumab and 21 (33%) patients had received lapatinib prior to T-DM1. Patients had received a median of three regimens prior to T-DM1 for metastatic breast cancer. The response rate of patients on T-DM1 was 35%, the clinical benefit rate was 49%, and median time to treatment failure (TTF) was 4.0 months. In 41 patients pretreated with pertuzumab, the response rate was 29%, the clinical benefit rate was 46%, and median TTF was 5.0 months. In 14 patients with brain metastases, median TTF was 6.0 months, although none achieved CR or PR for brain tumors. The most commonly reported grade 3 or 4 adverse event was thrombocytopenia, which was experienced by 13 (21%) patients, although this was not associated with severe bleeding. Treatment termination was necessary in 5 (8%) patients because of side effects. Conclusion: T-DM1 is an effective and well-tolerated treatment for patients with HER2-positive metastatic breast cancer that had progressed after previous anti-HER2 therapies. T-DM1 could be used for patients who have experienced progression following prior treatment with pertuzumab.

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