Therapy Adapted for High Risk and Low Risk HIV-Associated Anal Cancer

This phase II trial studies the side effects of chemotherapy and intensity modulated radiation therapy in treating patients with low-risk HIV-associated anal cancer, and nivolumab after standard of care chemotherapy and radiation therapy in treating patients with high-risk HIV-associated anal cancer. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. Chemotherapy drugs, such as mitomycin, fluorouracil, and capecitabine, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving chemotherapy with radiation therapy may kill more tumor cells. Immunotherapy with monoclonal antibodies, such as nivolumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving nivolumab after standard of care chemotherapy and radiation therapy may help reduce the risk of the tumor coming back.