Tucatinib, Trastuzumab, and Capecitabine With SRS for Brain Metastases From HER-2 Positive Breast Cancer

"SRS and oral tucatinib for 2 wk, followed by oral tucatinib, oral capecitabine, and intravenous (IV) trastuzumab maintenance during 21-d cycles until tumor progression, participant withdrawal, a severe adverse event deemed related to the study drug, or the treating physician discontinues the drug. There are three dosing levels of tucatinib (Dose Level 0, Dose Level -1, or Dose Level -2) using a dose de-escalation scheme. Dosing of capectabine (1000 mg/m2 BID Days 1-14) and trastuzumab (6 mg/kg once per 21 days; 8 mg/kg initial loading dose) per cycle will remain the same regardless of tucatinib dosing.~Dose Level 0: 300 mg twice a day (BID) continuously for 2 wk post SRS, then 300 mg BID continuously per cycle.~Dose Level -1: 250 mg twice a day (BID) continuously for 2 wk post SRS, then 250 mg BID continuously per cycle.~Dose Level -2: 200 mg twice a day (BID) continuously for 2 wk post SRS, then 200 mg BID continuously per cycle."