A Safety Study Adding Niraparib and Dostarlimab to Radiation Therapy for Rectal Cancers

Niraparib is a drug FDA-approved for use in maintenance treatment of adults with advanced ovarian cancer, fallopian tube cancer, or primary peritoneal cancer.

Dostarlimab, sold under the brand name Jemperli, is a monoclonal antibody medication used for the treatment of endometrial cancer.

Participants will be treated with intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) to minimize mean dose to femoral, pelvic, and lumbar bone marrow. The entire mesorectum will be treated to a total dose of 25 Gy.