ERBB3 and breast cancer: Currently, we only have preliminary data available for this agent in patients with heavily pretreated HER3 expressing metastatic breast cancer, demonstrating an ORR of 30.1% in HR+/HER2-negative breast cancer, 22.6% in HER3 high TNBC and 42.9% in HER3 high HER2-positive breast cancer.88 TOT-HER3 [NCT04610528] is a single-arm window-of-opportunity study investigating the response to patritumab deruxtecan in patients with HR+/HER2-negative breast cancer with tumors greater than or equal to 1 cm in size in the early-stage setting.