Bortezomib, Fluorouracil, and External-Beam Radiation Therapy in Treating Patients With Stage II, Stage III, or Stage IV Rectal Cancer

RATIONALE: Bortezomib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth and by blocking blood flow to the tumor. Drugs used in chemotherapy, such as fluorouracil, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving bortezomib and fluorouracil together with radiation therapy may kill more tumor cells.
PURPOSE: This phase I trial is studying the side effects and best dose of bortezomib when given together with fluorouracil and external-beam radiation therapy in treating patients with stage II, stage III, or stage IV rectal cancer.