Male and female patients age ≥ 18 years with pre-treated HER2-positive unresectable locally advanced or metastatic breast cancer (MBC) with a low affinity CD16A (FcγRIIIA) germline genotype (F/F or F/V allele) that are not candidates for curative intent.~The number of patients to be included is 41. The primary objective is to assess the efficacy, as determined by overall response rate (ORR), of the combination of margetuximab and tucatinib plus capecitabine.~After signing ICF and confirmed eligibility, patients will receive the combination of margetuximab 15 mg/kg by intravenous infusion on Day 1 of each cycle (no loading dose is required), capecitabine at 1000 mg per square meter of body-surface area orally twice daily on days 1 to 14 of each 21-day cycle, and tucatinib 300 mg orally twice daily (every 12 hours) continuously in 21-day cycles.~During the study, no further chemotherapy, hormonotherapy, radiotherapy, immunotherapy, or experimental drugs will be allowed.~Patients will receive treatment until disease progression, unacceptable toxicity, death, or discontinuation from the study treatment for any other reason.~Patients discontinuing the study treatment period will enter a post-treatment follow-up period during which survival and new anti-cancer therapy information will be collected every three months (± 14 days) from the last dose of investigational product until the end of study (EoS).
This is a multicenter, open-label, single-arm, phase II clinical trial to evaluate the efficacy and safety of margetuximab in combination with tucatinib and capecitabine in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer.