Phase IIa Trial of Trastuzumab Emtansine With Pertuzumab for Patients With Human Epidermal Growth Factor Receptor 2–Positive, Locally Advanced, or Metastatic Breast Cancer

Purpose Our phase IIa study characterized the safety and efficacy of two human epidermal growth factor receptor 2 (HER2) –targeted agents, trastuzumab emtansine (T-DM1) and pertuzumab, in patients with HER2-positive metastatic breast cancer (MBC). Patients and Methods Patients with HER2-positive locally advanced breast cancer or MBC were treated with 3.6 mg/kg T-DM1 plus pertuzumab (840-mg loading dose, then 420 mg subsequently) once every 3 weeks. The primary efficacy end point was investigator-assessed objective response rate (ORR). Results Sixty-four patients (43 patients in the second-line or greater setting [advanced MBC]; 21 patients in the first-line setting [first-line MBC]) were enrolled. Patients with advanced MBC had received trastuzumab and a median of six prior nonhormonal treatments for MBC; 86% of first-line MBC patients had received trastuzumab in the (neo)adjuvant setting. The ORR was 41% overall, 33% in patients with advanced MBC, and 57% in first-line patients. Median progression-free s...