RC0639: Phase II study of paclitaxel, trastuzumab, and lapatinib as adjuvant therapy for early stage HER2-positive breast cancer

Lapatinib adds to the efficacy of trastuzumab in preclinical models and also in the neo-adjuvant setting. This study assesses the safety and feasibility of adding lapatinib to paclitaxel and trastuzumab (THL) as part of the adjuvant therapy for HER2-positive breast cancer (HER2+ BC). In this single-arm phase II study, patients with stages I-III HER2+ BC received standard anthracycline-based chemotherapy followed by weekly taxane, with concurrent standard trastuzumab, plus daily lapatinib for a total of 12 months. The primary endpoint was symptomatic congestive heart failure, secondary endpoints included overall safety. A total of 109 eligible patients were enrolled. Median follow-up is 4.3 years. No patients experienced congestive heart failure while on treatment. Mean left ventricular ejection fraction at baseline and at the end of THL were 63.6 % (N = 109, SD = 5.7) and 59.8 % (N = 98, SD = 8.1), respectively [mean change -3.95 % (N = 98, SD = 8.3), p < 0.001]. One hundred and two patients initiated post-AC treatment; of them, 31 % experienced grade 3 (no G4) diarrhea with lapatinib at 750 mg/day. The addition of lapatinib to paclitaxel and trastuzumab following AC does not add cardiac toxicity. Lapatinib dose of 750 mg/day in combination with standard chemotherapy plus trastuzumab has acceptable overall tolerability.