A Study of Neoadjuvant Dostarlimab Plus Capecitabine Plus Oxaliplatin (CAPEOX) Vs CAPEOX With Previously Untreated T4N0 or Stage III Mismatch Repair Proficient (MMRp)/Microsatellite Stable (MSS) Colon Cancer

Prior treatment

• Has received prior medical therapy (chemotherapy, immunotherapy, biologic, or targeted therapy), radiation therapy or surgery for management of colon cancer
• Has, in the investigator's opinion, a tumor that is not amenable to surgery or has any other contraindication to surgery
• Has received treatment with an investigational agent within \[4 weeks\] of the first dose of study intervention

Other illness

• Has distant metastatic disease
• Has any history of interstitial lung disease or immune-related pneumonitis
• Is considered, in investigator's opinion, a poor medical risk due to a serious, uncontrolled medical disorder, non-malignant systemic disease, or active infection requiring systemic therapy
• Has a history of severe allergic and/or anaphylactic reactions to chimeric, human, or humanized antibodies, fusion proteins, or known allergies to dostarlimab, or its excipients, or any components of CAPEOX

Lab values

• Has experienced any of the following with prior immunotherapy: any imAE ≥ Grade 3, immune-mediated severe neurologic events of any-grade (e.g., myasthenic syndrome/myasthenia gravis, encephalitis, Guillain Barré Syndrome, or transverse myelitis), exfoliative dermatitis of any grade \[Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), or Drug rash with eosinophilia and systemic symptoms (DRESS) syndrome\], or myocarditis of any grade. Non-clinically significant laboratory abnormalities are not exclusionary
• Has a history or current evidence of any medical condition, therapy, or laboratory abnormality that might confound the study results, interfere with their participation for the full duration of the study intervention, or indicate it is not in the best interest of the participant to participate, in the opinion of the investigator

Other

• Is pregnant or breastfeeding

• Has untreated pathologically confirmed colon adenocarcinoma
• Has resectable colon adenocarcinoma defined as clinically T4N0 or Stage III
• Has a tumor demonstrating the presence of either-
  • MMR status: MMR status must be assessed by Immunohistochemistry (IHC) for MMR protein expression (MLH1, MSH2, MSH6, PMS2) where all proteins are present indicates MMRp; MMR status may be determined local laboratory; or
  • MSS or Microsatellite Instability-L (MSI-L) phenotype as determined by polymerase chain reaction (PCR) or by tissue next generation sequencing (NGS), determined by local laboratory
• Provides fresh tumor tissue obtained during either the pre-screening or screening period via colonoscopy performed per procedure manual. Tissue biopsy is required
• Is willing to use adequate contraception male and/or female participants
• Has an Eastern Cooperative Oncology Group - Performance status (ECOG-PS) of 0 or 1
• Has adequate organ function