Robust in vivo activity of VRN101099 was observed in HER2-positive BT474 xenograft models. Moreover, once daily oral administration of VRN101099 significantly regressed intracranial BT474 tumor, demonstrating greater efficacy...In summary, VRN101099 is a brain penetrant, orally bioavailable, irreversible, and highly selective inhibitor of HER2 with therapeutic potential in HER2-positive BCBM. These data support the clinical development of VRN101099 in HER2-driven cancers.