Safety and Efficacy Assessment of Trastuzumab Emtansine in Indian Patients With Human Epidermal Growth Factor Receptor 2‐Positive Unresectable Locally Advanced or Metastatic Breast Cancer Previously Treated With Trastuzumab and a Taxane: An Open‐Label, Single‐Arm, Phase IV Study

ABSTRACT Introduction Trastuzumab emtansine (T‐DM1), an antibody–drug conjugate, targets tumor cells overexpressing human epidermal growth factor receptor 2 (HER2). This single‐arm, phase IV study assessed the safety and efficacy of T‐DM1 in Indian patients with HER2‐positive, locally advanced, or metastatic breast cancer previously treated with trastuzumab and a taxane. Methods Patients received T‐DM1 (3.6 mg/kg intravenously every 3 weeks) until death, disease progression, unacceptable toxicity, consent withdrawal, or up to a maximum of 12 months after the last patient's first visit, whichever occurred first. Safety was mainly assessed by the incidence and severity of adverse events (AEs). Efficacy was evaluated by progression‐free survival (PFS), overall survival (OS), and overall response rate (ORR). Patients were followed up posttreatment until 12 months or until lost to follow‐up, withdrawn consent, or death. Results A total of 70 eligible patients (median age range: 50.0 27.0–75.0 years) received at least one dose of T‐DM1 (median duration range: 32.0 1.0–125.0 weeks). Adverse events in 21 (30.0%) patients were treatment‐related. The most common treatment‐related AEs and SAEs were thrombocytopenia (seven 10.0% and three 4.0% patients, respectively) and epistaxis (four 6.0% and two 3.0% patients, respectively). During the study, 10 (18.0%) patients died (disease progression: n = 6; AE: n = 3; and unknown reason: n = 1), while 2 patients died during the follow‐up period. Median PFS was 14 months (95% confidence interval CI: 8.0, 17.0). Among 65 evaluable patients, 16 (23.0%) achieved partial responses; ORR was 23.0%. Conclusions Trastuzumab emtansine was found to be safe and efficacious in the Indian patients.