Combined Modality Therapy for Patients With With HIV and Stage I, Stage II, or Stage III Anal Cancer

RATIONALE: Drugs used in chemotherapy, such as cisplatin and fluorouracil, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as cetuximab, can block tumor growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry tumor-killing substances to them. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving cisplatin, fluorouracil, and cetuximab together with radiation therapy may kill more tumor cells. PURPOSE: This phase II trial is studying how well giving cisplatin, fluorouracil, and cetuximab together with radiation therapy works in treating patients with HIV and stage I, stage II, or stage III anal cancer.