Beamion BCGC-1: A Phase Ib Dose Escalation and Phase II Dose Optimization, Randomized, Open-label, Multicenter Trial of Oral Zongertinib (BI 1810631) in Combination With Intravenous Trastuzumab Deruxtecan (T-DXd) or in Combination With Intravenous Trastuzumab Emtansine (T-DM1) for Treatment of Patients With Advanced HER2+ Metastatic Breast Cancer (mBC) and Metastatic Gastric, Gastroesophageal Junction, or Esophageal Adenocarcinoma (mGEAC)