Sulfasalazine in Preventing Acute Diarrhea in Patients With Cancer Who Are Undergoing Pelvic Radiation Therapy

DISEASE CHARACTERISTICS: * Diagnosis of cancer that supports the use of radiotherapy to the pelvis * No current or prior metastases beyond pelvic regional lymph nodes * Planning to receive a course of continuous definitive or adjuvant external-beam radiotherapy to a minimum dose of 4500 cGy with or without fluorouracil, capecitabine, or oxaliplatin * Planned course of pelvic radiotherapy must fall within the following parameters: * Pelvis must be encompassed by the planned radiotherapy fields * Superior border may not lie superior to the L4-5 interspace and may not be inferior to the most inferior aspect of the sacroiliac joints * Portions of the rectum may have special blocking, depending upon disease site * Total planned dose to the central axis midplane (for AP-PA parallel opposed fields) or isocenter (for 3- or 4-field techniques) for the pelvic field must lie between 4500-5300 cGy (inclusive)\* * Subsequent to completion of treatment to the pelvic field, a boost to primary tumor or tumor bed may be planned * Planned treatment is to be given 4-5 times per week on a one-treatment-per-day basis * Daily dose (specified at central axis midplane or at isocenter for multi-field techniques) must lie between 170-210 cGy (inclusive) per day\* * NOTE: \*For institutions that do not use midplane or isocenter as the point for specification of dose, it will be necessary to determine the dose according to the methods specified above in order to determine patient eligibility. * No perineal irradiation planned (e.g., anal cancer patients, patients who have had an abdominal-perineal resection) * No brachytherapy planned before the completion of all external-beam radiotherapy * No planned split-course radiotherapy PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Life expectancy ≥ 6 months * Hemoglobin ≥ 10.0 g/dL * Leukocytes ≥ 3,500/mm\^3 * ANC ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Creatinine ≤ 1.5 times upper limit of normal (ULN) * AST ≤ 1.5 times ULN * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Willing to provide blood specimens as required by the study (Mayo Clinic Rochester patients only) * Able to complete questionnaires alone or with assistance * No history of inflammatory bowel disease * No history of gastrointestinal or genitourinary obstruction or porphyria * No history of G6PD deficiency * No history of irritable bowel syndrome * No history of blood dyscrasia * No history of severe allergies or asthma * No history of hepatic or renal disease * No diarrhea ≥ grade 3, rectal bleeding, abdominal cramping, or incontinence of stool within the past week * No medical condition that may interfere with the ability to receive study treatment * No known allergy to sulfasalazine, sulfa medications, salicylates, or any known component of drug formulation PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No prior pelvic radiotherapy * No prior abdominal-perineal resection, Hartmann procedure, or other surgical procedure leaving the patient without a functioning rectum * No planned use of leucovorin or cytotoxic chemotherapeutic agents concurrent with radiotherapy (except for fluorouracil, capecitabine, or oxaliplatin) * No other concurrent sulfasalazine * No concurrent digoxin