Asciminib in HER2+ Breast Cancer Brain Metastases

Each study treatment cycle will last 21 days. Asciminib will be taken orally every day during the treatment period at the dose determined as the MTD during the safety lead-in in combination with trastuzumab at a standard dose of 6mg/kg IV. Asciminib dose will begin at 80 mg daily (dose level 1), with a potential range from 40 mg daily (dose level -1A, with trastuzumab) to 200 mg bid (dose level 3, with trastuzumab) depending on the results of the safety lead-in. Trastuzumab will be given intravenously (IV) or subcutaneously (SQ) on Day 1 of each 21 day cycle.