S0304 Induct Chemo Then Chemo-RT in Pts w/Locally Advanced Adenocarcinoma of the Rectum

DISEASE CHARACTERISTICS: * Histologically confirmed primary adenocarcinoma of the rectum * Locally advanced disease (clinical T3-4, N0-2, M0) based on at least 1 of the following criteria: * Clinically fixed tumors on rectal examination with tumor adherent to the pelvic sidewall and/or sacrum * Sciatica attributed to sacral root invasion with CT scan/MRI evidence of the lack of clear tissue plane is considered evidence of fixation * Hydronephrosis on CT scan or intravenous pyelogram of ureteric or bladder invasion by cystoscopy and cytology or biopsy * Invasion into the prostate, vagina, or uterus * Transmural penetration of tumor through the muscularis propria as evidenced by CT scan or MRI and endorectal ultrasound * Distal border of the tumor must be at or below the peritoneal reflection (within 12 cm of the anal verge) by proctoscopic examination * Measurable disease by x-ray, scans, or physical examination * Available tumor tissue to determine molecular profile of the tumor before study treatment * No clinical evidence of high-grade (lumen diameter \< 1 cm) large bowel obstruction unless a diverting colostomy has been performed PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Zubrod 0-2 Life expectancy * Not specified Hematopoietic * WBC ≥ 3,500/mm\^3 * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥100,000/mm\^3 Hepatic * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * SGOT or SGPT ≤ 2.5 times ULN * Alkaline phosphatase…