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

Inclusion Criteria: * Capable of understanding and complying with the protocol requirements and have signed the informed consent document. Patients with mild cognitive impairment may be considered for enrollment in the study if their legally authorized representative provides written informed consent for the patient. * 18 years or older in age * Biopsy proven dMMR (by IHC), Stage II or III colon cancer per CT imaging correlation with AJCC 8th edition, 2017, amendable to en block surgical resection as determined by colorectal surgeon. * Biopsy specimen for diagnosis of dMMR Colon cancer should have enough tissue for minimum 4 and max 6 adjacent unstained FFPE slides (4µm each) as determined by Protocol Pathologist Dr. Anthony Snow for CD3+ and CD8+ analysis. If there is not enough tissue present in original sample, a repeat colonoscopy and biopsy may be performed; otherwise patient is not eligible. * Potentially surgically resectable Stage II or III patients who are willing to forgo surgical resection if study endpoints are met. Patient with easily manageable bowel changes amenable to laxatives or stool softeners as outpatient per assessment by colorectal surgery are allowed. (See exclusion criteria #2) * ECOG performance status less than or equal to 1 * Absence of metastatic disease on CT CAP with Contrast within 28 days from treatment start * Absolute neutrophil count greater than or equal to 1,500/µL * Platelets greater than or equal to 100,000/µL * Hemoglobin greater than…