Single Arm Study of Neoadjuvant Dostarlimab in Stage II and III Deficient Mismatch Repair Colon Cancers

This trial tests whether giving the immunotherapy drug dostarlimab before surgery can shrink — or even eliminate — stage II and III colon cancer tumors that have a specific genetic feature called dMMR (deficient mismatch repair). If the tumor disappears completely, surgery might be avoided. **You may be eligible if...** - You are 18 or older with a biopsy-confirmed diagnosis of stage II or III dMMR colon cancer - Your cancer can be surgically removed - You are willing to possibly skip surgery if the cancer disappears after treatment - Your blood counts, liver, and kidney function are within acceptable ranges **You may NOT be eligible if...** - You have more than one primary colon tumor at the same time - Your tumor is causing a life-threatening blockage or severe bleeding - You have had a prior organ transplant - You have an active autoimmune disease or immunodeficiency - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.