Study of Petosemtamab Plus Chemotherapy Versus Cetuximab Plus Chemotherapy in RAS and BRAF Wild-type, Unresectable or Metastatic, Left-sided Colorectal Cancer

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.