Cemiplimab With or Without Fianlimab to Treat Older Patients With Localized or Locally Advanced MSI-H Colorectal Cancer

Inclusion Criteria for Cohort A and B: * Age ≥70 years. * Eastern Cooperative Oncology Group (ECOG) performance status 0 -2 * Have histologically proven localized or locally advanced mismatch repair deficient (dMMR) or microsatellite unstable (MSI-H) colorectal cancer. * Must not have received any prior systemic treatment or radiation. * Must be agreeable to endoscopic, and CT surveillance for a total of 24 months. * Patient's acceptance to have a tumor biopsy. * Patients must have adequate organ and marrow function defined by study-specified laboratory tests and procedures. * LVEF assessment with documented LVEF ≥ 45% by either TTE or MUGA (TTE preferred) within 6 months from first study drug administration. * For both Women and Men, must use acceptable form of birth control while on study. * Ability to understand and willingness to sign a written informed consent document. Inclusion Criteria for Cohort C and D: * Age ≥18 years. * Eastern Cooperative Oncology Group (ECOG) performance status 0 -3. * Have histologically proven localized or locally advanced mismatch repair deficient (dMMR) or microsatellite unstable (MSI-H) colorectal cancer. * Patient deemed a poor surgical candidate after evaluation by a surgeon or unwilling to undergo surgery. * Must not have received any prior systemic treatment or radiation. * Must be agreeable to endoscopic, and CT surveillance for a total of 24 months. * Patient's acceptance to have a tumor biopsy. * Patients must have adequate organ …