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)

This study is open to adults aged 18 years and older with different types of HER2+ cancer that has spread and cannot be removed by surgery. People can take part in this study if their tumours show HER2 aberrations and previous treatment was not successful. The purpose of this study is to find a suitable dose of zongertinib that people with different types of HER2+ cancer that has spread can tolerate best when taken together with trastuzumab deruxtecan (T-DXd) or with trastuzumab emtansine (T-DM1). Another purpose is to check whether zongertinib in combination with T-DXd or with T-DM1 can make tumours shrink. Zongertinib inhibits HER2. HER2 causes cancer cells to grow.

The study is split into treatment cycles. All study participants are treated with zongertinib in combination with T-DXd or with T-DM1. This study has 2 parts. In Part 1, participants receive increasing doses of zongertinib. In Part 2, participants are put into different groups by chance. Each group receives a different dose of zongertinib. Every participant has an equal chance of being in each group.

During the study, the participants visit the study site regularly. In this study, researchers want to find the highest dose of zongertinib that participants can tolerate when taken together with T-DXd or with T-DM1. To find this out, researchers look at certain severe health problems that a number of participants have. The doctors regularly check the size of the tumour with imaging methods (CT/MRI) during the study. The doctors also regularly check participants' health and take note of any unwanted effects.