This study investigates the effectiveness of combination chemotherapy with an investigational medication compared to chemotherapy alone in patients with stage III colon cancer. The focus is on patients with a specific condition called deficient DNA mismatch repair (dMMR), which is when the body's natural ability to fix DNA mistakes is not working properly. The purpose of this study is to see if adding the investigational medication can improve the time patients remain free of cancer.
Participants will receive a combination of chemotherapy drugs, including oxaliplatin, leucovorin calcium, and fluorouracil, known as FOLFOX. Some participants will also receive an investigational medication along with FOLFOX, and then continue with the investigational medication alone. The study will compare the outcomes of these two groups to determine the effectiveness of the additional treatment.
- Who can participate: Adults with stage III colon cancer and specific DNA mismatch repair deficiencies can participate. Tumors must be confirmed by laboratory tests, and participants must meet other health criteria.
- Study details: Participants will receive chemotherapy drugs, and some will also receive an investigational medication. A placebo is not used.

