On March 13, 2007, the U.S. Food and Drug Administration approved lapatinib (Tykerb tablets; GlaxoSmithKline, Philadelphia), an oral, small molecule, dual tyrosine kinase inhibitor of ErbB-2 and ErbB-1, for use in combination with capecitabine for the treatment of patients with human epidermal growth factor receptor (HER)-2-overexpressing metastatic breast cancer who had received prior therapy including an anthracycline, a taxane, and trastuzumab. One multicenter, open-label, randomized trial was submitted. Eligible patients had stage IIIb or IV breast cancer, ErbB-2 overexpression (immunohistochemistry 3+ or 2+ with fluorescence in situ hybridization confirmation), measurable disease, a 0 or 1 Eastern Cooperative Oncology Group performance status score, a cardiac ejection fraction within the institutional normal range, and adequate laboratory function. Patients received either lapatinib (1,250 mg once daily on days 1-21) plus capecitabine (1,000 mg/m(2) every 12 hours on days 1-14) every 21 days or capecitabine alone (1,250 mg/m(2) every 12 hours on days 1-14) every 21 days. The primary endpoint was time to progression (TTP) determined by a blinded independent review panel. After TTP results of a prespecified interim analysis were made available, study enrollment was discontinued (399 patients enrolled). The median TTP was 27.1 versus 18.6 weeks (hazard ratio, 0.57; p = .00013) favoring the lapatinib plus capecitabine arm. Response rates were 23.7% (lapatinib plus capecitabine) versus 13.9% (capecitabine alone). Survival data were not mature. Although the toxicities observed in the lapatinib and capecitabine combination arm were generally similar to those in the capecitabine alone arm, a higher incidence of diarrhea and rash was noted with the combination. Grade 3 or 4 adverse reactions that occurred with a frequency of >5% in patients on the combination arm were diarrhea (13%) and palmar-plantar erythrodysesthesia (12%). There was a 2% incidence of reversible decreased left ventricular function in the combination arm.