Neoadjuvant Celecoxib and Capecitabine Combined With Pelvic Irradiation in Treating Patients With Stage II or Stage III Adenocarcinoma (Cancer) of the Rectum

RATIONALE: Celecoxib may stop the growth of tumor cells by blocking the enzymes necessary for their growth. Drugs used in chemotherapy, such as capecitabine, work in different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Celecoxib may also make tumor cells more sensitive to chemotherapy and radiation therapy. Giving celecoxib with capecitabine and radiation therapy before surgery may shrink the tumor so that it can be removed.
PURPOSE: This phase II trial is studying how well giving neoadjuvant celecoxib together with capecitabine and pelvic irradiation works in treating patients with stage II or stage III adenocarcinoma (cancer) of the rectum.