mFOLFOX6

The purpose of this trial is to evaluate how well petosemtamab in combination with chemotherapy works against colorectal cancer located on the left side of the colon that cannot be safely removed by surgery or has spread to other parts of the body. Participants will receive either petosemtamab + doctor's choice of chemotherapy (mFOLFOX6 or FOLFIRI) or standard-of-care cetuximab + doctor's choice of chemotherapy (mFOLFOX6 or FOLFIRI). No participants will be given placebo. The treatment duration will be different for every participant. If a participant's cancer stays the same or gets better, and there are not any serious problems, participants can keep getting study treatment for as long as the study is open. Participants will be asked to attend 2 visits at the study clinic for each cycle (duration of cycle is 4 weeks). During visits, there will be various tests (such as blood draws) and procedures (such as imaging) to monitor whether the study treatment is safe and effective. The overall study duration (including screening, treatment, and follow-up) will be different for every participant.

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), with trastuzumab emtansine (T-DM1), with trastuzumab and capecitabine, with zanidatamab, or with mFOLFOX6 (with or without trastuzumab). Another purpose is to check whether zongertinib alone and in combination with other treatments can make tumours shrink. Zongertinib inhibits HER2. HER2 causes cancer cells to grow. In this study, participants receive treatment in cycles. Study participants are treated with zongertinib alone or in combination with other treatments. This study has 2 parts. In Part 1, participants in different groups 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 other treatments. 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.