A Study of Dostarlimab in Participants With Untreated Locally Advanced Rectal Cancer in China

Inclusion Criteria: * Participant has histologically confirmed Stage II to III (T3-T4, N0, or T any, N+), locally advanced rectal adenocarcinoma * Participant has radiologically and endoscopically evaluable disease * Participant has a tumor which can be categorized as dMMR or MSI-H by central assessment Exclusion Criteria: * Participant has distant metastatic disease * Participant has received prior radiation therapy, systemic therapy, or surgery for management of rectal cancer * Has a known additional malignancy that progressed or required active treatment within the past 2 years * Has an active autoimmune disease that has required systemic treatment in the past 2 years * Has experienced any of the following with prior immunotherapy: any irAE ≥ Grade 3, immune-related severe neurologic events of any-grade (e.g., myasthenic syndrome/myasthenia gravis, encephalitis, Guillain Barré Syndrome, or transverse myelitis), exfoliative dermatitis of any grade \[SJS (Stevens-Johnson Syndrome, TEN (Toxic Epidermal Necrolysis), DRESS (Drug rash with eosinophilia and systemic symptoms)\], or myocarditis of any grade. Non-clinically significant laboratory abnormalities are not exclusionary * Has any history of interstitial lung disease or pneumonitis * Has received or plans to receive an organ or stem cell transplant that uses donor stem cells (allogeneic stem cell transplant) * 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