This clinical trial is investigating the use of an immunotherapy drug called **toripalimab** for patients who have had surgery for a type of colon cancer known as **mismatch repair deficient (dMMR) stage IIB, IIC, or III**. **Immunotherapy** is a treatment that helps the body's immune system fight cancer. The main goal is to see if toripalimab can help prevent the cancer from coming back over three years. Participants will receive toripalimab through an IV (intravenous) every three weeks for six months, totaling eight doses, as long as the cancer does not return and side effects are manageable. **Key Points:** - **Duration and Visits**: The study treatment lasts 6 months with follow-ups every 6 months for 5 years. - **Compensation**: Details about compensation are not provided. - **Risks**: Possible immune-related side effects, which will be closely monitored. Eligibility includes patients who have had a full colon cancer resection and meet specific health criteria. Participants must not have any other major health issues that could interfere with the study. Frequent check-ups and tests, including CT scans and blood tests, will be required.