This study explores using **dostarlimab** before and after surgery for people with a certain type of colon cancer. Colon cancer is a disease where bad cells grow in the colon, part of your digestive system. **Dostarlimab** is a medicine that helps the immune system find and fight cancer cells. The study compares dostarlimab with the usual treatment for people with T4N0 or Stage III colon cancer. This specific cancer has a problem called **dMMR/MSI-H**, making it hard for cells to fix mistakes in their DNA, which can lead to cancer.

• This study is for people who have not yet received any treatment for their cancer.
• Participants must have a specific type of colon cancer that can be removed with surgery.
• Pregnant women or those planning to have a baby cannot join.

Participants will be monitored to see how well dostarlimab works in stopping cancer from coming back after surgery. This study might help in finding better ways to treat colon cancer.