Intensity-Modulated Radiation Therapy, Fluorouracil, and Mitomycin C in Treating Patients With Invasive Anal Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed carcinoma of the anal canal, including any of the following subtypes: * Squamous cell * Basaloid * Cloacogenic * Primary invasive disease * T2-4, N0-3 disease * Clinically positive small inguinal nodes (i.e., \< 1 cm in size) must be confirmed by biopsy (preferably fine-needle aspiration) within the past 6 weeks * Biopsy is not required for enlarged inguinal, perirectal, or pelvic nodes on exam or CT scan that are found to be ≥ 1.0 cm and are considered to be clinically positive PATIENT CHARACTERISTICS: * Zubrod performance status 0-1 * Hemoglobin ≥ 8.0 g/dL (transfusion or other intervention allowed) * ALT and AST \< 3 times upper limit of normal * Absolute neutrophil count ≥ 1,800/mm³ * Serum creatinine ≤ 1.5 mg/dL * Platelet count ≥ 100,000/mm³ * Bilirubin \< 1.4 mg/dL * WBC ≥ 3,000/mm³ * INR ≤ 1.5 * No known AIDS * HIV-positive patients without AIDS are eligible * HIV test required for patients with clinical suspicion of AIDS * No other invasive malignancy within the past 3 years except for nonmelanomatous skin cancer * No severe, active comorbidity, defined as any of the following: * Unstable angina and/or congestive heart failure requiring hospitalization within the past 6 months * Transmural myocardial infarction within the past 6 months * Acute bacterial or fungal infection requiring IV antibiotics * Chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring…