A Study of Tucatinib (MK-7119) in Combination With Trastuzumab and Capecitabine in Participants With Previously Treated Locally Advanced Unresectable or Metastatic Human Epidermal Growth Factor Receptor 2 Positive (HER2+) Breast Carcinoma (MK-7119-001)

The goal of this study is to evaluate the efficacy and safety of tucatinib in combination with trastuzumab and capecitabine in participants with unresectable locally advanced or metastatic HER2+ breast cancer who have had prior treatment with taxane anti-cancer agent, trastuzumab, pertuzumab and trastuzumab emtansine (T-DM1). The primary hypothesis is that the confirmed objective response rate (cORR) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) as determined by independent central review (ICR) for the combination of tucatinib, trastuzumab and capecitabine, is greater than 20%.