Trastuzumab emtansine in HER2-positive metastatic breast cancer after pertuzumab and trastuzumab: TDM1RM Study

Abstract

Background: Trastuzumab emtansine (TDM1) is indicated for the treatment of metastatic HER2-positive breast cancer (HMBC) after progression on prior trastuzumab and taxane (TT). There are few data on its efficacy after pertuzumab, trastuzumab and taxane (PTT). The present study is a regional multicenter retrospective evaluation of the activity of TDM-1 after front line pertuzumab based therapy. Methods: All three oncology centers of “Region de Murcia” participated in a restrospective observational study. Patients diagnosed with HMBC treated with a minimum of 2 cycles of TDM1 after PTT were included. Efficacy and safety were analysed and compared with TH3RESA and EMILIA study. Results: Between Feb 2015 until Apr 2020, 52 patients with HMBC were treated with TDM1 after PTT. After a median of follow-up of 33 months, 8 patients were still under TDM1 therapy and 30 patients (58%) have died at the end of the study. Median progression free survival (PFS) was 8,4 months (95% IC 6,9 – 9,9) and median overal survival (OS) was 23,6 months (95% IC 17,5 – 29,7). Overall Rate Response (ORR) was 42%. The most frequent grade 3 toxicity was thrombocytopenia (8%) (see table). No dose-limiting cardiotoxicity was seen. Conclusions: T-DM1 was an effective and well-tolerated treatment in routine clinical practice in patients with HMBC after PTT. ORR, PFS and OS were similar than pivotal study after only trastuzumab-taxane. We observed a similar toxicity of TDM1. We had a higher incidence of brain metastases.