A Phase II Study of Trastuzumab Emtansine in Patients With Human Epidermal Growth Factor Receptor 2–Positive Metastatic Breast Cancer Who Were Previously Treated With Trastuzumab, Lapatinib, an Anthracycline, a Taxane, and Capecitabine

Purpose To determine whether the antibody-drug conjugate trastuzumab emtansine (T-DM1), which combines human epidermal growth factor receptor 2 (HER2) –targeted delivery of the potent antimicrotubule agent DM1 with the antitumor activity of trastuzumab, is effective in patients with HER2-positive metastatic breast cancer (MBC) who have previously received all standard HER2-directed therapies. Patients and Methods In this single-arm phase II study, T-DM1 3.6 mg/kg was administered intravenously every 3 weeks to patients with HER2-positive MBC who had prior treatment with trastuzumab, lapatinib, an anthracycline, a taxane, and capecitabine. The primary objectives were overall response rate (ORR) by independent review and safety. Results Among 110 pretreated patients (median, seven prior agents for MBC; median follow-up, 17.4 months), the ORR was 34.5% (95% CI, 26.1% to 43.9%), clinical benefit rate was 48.2% (95% CI, 38.8% to 57.9%), median progression-free survival (PFS) was 6.9 months (95% CI, 4.2 to 8.4 ...