[Show abstract][Hide abstract] ABSTRACT: Overexpression of human epidermal growth factor receptor-2 (HER2) in metastatic breast cancer (MBC) is associated with poor prognosis. This single-arm open-label trial (EGF109491; NCT00508274) was designed to confirm the efficacy and safety of lapatinib in combination with capecitabine in 52 heavily pretreated Chinese patients with HER2-positive MBC. The primary endpoint was clinical benefit rate (CBR). Secondary endpoints included progression-free survival (PFS), time to response (TTR), duration of response (DoR), central nervous system (CNS) as first site of relapse, and safety. The results showed that there were 23 patients with partial responses and 7 patients with stable disease, resulting in a CBR of 57.7%. The median PFS was 6.34 months (95% confidence interval, 4.93-9.82 months). The median TTR and DoR were 4.07 months (range, 0.03-14.78 months) and 6.93 months (range, 1.45-9.72 months), respectively. Thirteen (25.0%) patients had new lesions as disease progression. Among them, 2 (3.8%) patients had CNS disease reported as the first relapse. The most common toxicities were palmar-plantar erythrodysesthesia (59.6%), diarrhea (48.1%), rash (48.1%), hyperbilirubinemia (34.6%), and fatigue (30.8%). Exploratory analyses of oncogenic mutations of PIK3CA suggested that of 38 patients providing a tumor sample, baseline PIK3CA mutation status was not associated with CBR (P = 0.639) or PFS (P = 0.989). These data confirm that the lapatinib plus capecitabine combination is an effective and well-tolerated treatment option for Chinese women with heavily pretreated MBC, irrespective of PIK3CA status.