Beamion BCGC-1: A Study to Find a Suitable Dose of Zongertinib Used Alone and in Combination With Other Treatments to Test Whether it Helps People With Different Types of HER2+ Cancer That Has Spread

Inclusion criteria: * Patients ≥18 years of age or over the legal age of consent in countries where that is greater than 18 years at the time of signature of the informed consent form (ICF) * Cohorts A to K and Cohort O and P: Documented Human epidermal growth factor receptor 2 overexpressing and/or amplified (HER2+), metastatic breast cancer (mBC) or metastatic gastric adenocarcinoma, gastroesophageal junction adenocarcinoma, or esophageal adenocarcinoma (mGEAC). * Cohorts L (L-ext), M, and N (metastatic colorectal cancer (mCRC)): Documented Human epidermal growth factor receptor 2 (HER2) overexpression/amplification * For (Phase II): Patient must provide tumor tissue * History of prior treatment lines in palliative setting: For cohorts A, B, C, D, E, F, G, H, I, I-ext, J, J-ext, K, O and P documented investigator assessed progression * Presence of at least one measurable lesion according to RECIST 1.1 * Eastern Cooperative Oncology Group (ECOG) score of 0 or 1 * Adequate organ function based on laboratory values Further inclusion criteria apply. Exclusion criteria: * Mean resting corrected QT interval (QT interval corrected for heart rate by Fridericia´s formula (QTcF)) \>470 msec. * Any factors that increase the risk of QT interval corrected for heart rate (QTc) prolongation or risk of arrhythmic events such as heart failure, hypokalemia, congenital long QT syndrome, personal or family history of long QT syndrome or unexplained sudden death under 40 years-of-age. * Ejection fraction \<50% or the lower limit of normal of the institutional standard within 28 days prior to randomization * History of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required steroids, current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at screening Further exclusion criteria apply.