This phase II trial tests the effect of giving pembrolizumab in combination with radiation therapy after chemotherapy in preventing surgery to remove the bladder in patients with muscle invasive bladder cancer. Standard of care therapy includes chemotherapy before surgery (neoadjuvant) to shrink or get rid of the tumor. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the tumor, and may interfere with the ability of tumor cells to grow and spread. Radiation therapy uses high energy x-rays, particles, or radioactive seeds to kill cancer cells and shrink tumors. Photon beam radiation therapy is a type of radiation therapy that uses x-rays or gamma rays that come from a special machine called a linear accelerator. The radiation dose is delivered at the surface of the body and goes into the tumor and through the body. Giving pembrolizumab in combination with radiation therapy after neoadjuvant chemotherapy may help prevent surgical removal of the bladder in patients with muscle invasive bladder cancer.
Participants must have histologic evidence of cT2-T4aN0M0 muscle invasive urothelial carcinoma of the bladder within 180 days prior to starting neoadjuvant therapy (NAT)
Participants must have had CT chest/abdomen/pelvis (C/A/P), MRI C/A/P or PET within 60 days prior to starting NAT to determine cT2-T4aN0M0
Participants must have undergone TURBT with biopsy of areas of prior disease and systematic biopsies (left and right lateral, dome, posterior wall and trigone) and radiologic staging showing clinically T0-T1 disease within 60 days after the last dose of NAT. At least 4 out of 5 systematic biopsies must be performed
NOTE: This TURBT must be within 90 days prior to registration. Registration must be within 90 days after the last dose of NAT
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