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 centralassessment

Exclusion Criteria:

• Participant has distant metastatic disease

• Participant has received prior radiation therapy, systemic therapy, or surgery formanagement of rectal cancer

• Has a known additional malignancy that progressed or required active treatmentwithin the past 2 years

• Has an active autoimmune disease that has required systemic treatment in the past 2years

• Has experienced any of the following with prior immunotherapy: any irAE ≥ Grade 3,immune-related severe neurologic events of any-grade (e.g., myasthenicsyndrome/myasthenia gravis, encephalitis, Guillain Barré Syndrome, or transversemyelitis), exfoliative dermatitis of any grade [SJS (Stevens-Johnson Syndrome, TEN (Toxic Epidermal Necrolysis), DRESS (Drug rash with eosinophilia and systemicsymptoms)], or myocarditis of any grade. Non-clinically significant laboratoryabnormalities 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 donorstem 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 itsexcipients