Irinotecan and Celecoxib in Treating Patients With Unresectable or Metastatic Colorectal Cancer

DISEASE CHARACTERISTICS: Histologically confirmed colorectal cancer Metastatic or unresectable disease Failed first-line or second-line therapy OR recurred after receiving fluorouracil-based adjuvant chemotherapy No known brain metastases PATIENT CHARACTERISTICS: Age 18 and over Performance status ECOG 0-2 OR Karnofsky 60-100% Life expectancy More than 12 weeks Hematopoietic Absolute neutrophil count ≥ 1,500/mm^3 Platelet count ≥ 100,000/mm^3 WBC ≥ 3,000/mm^3 Hepatic AST and ALT ≤ 2.5 times upper limit of normal Bilirubin normal No Gilbert's disease Renal Creatinine normal OR Creatinine clearance ≥ 60 mL/min Cardiovascular No symptomatic congestive heart failure No unstable angina pectoris No cardiac arrhythmia Gastrointestinal Able to receive oral medications No prior inflammatory bowel disease No active ulcer disease or gastritis No contraindications for sigmoidoscopy No active colostomy Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 3 months after study participation No prior allergic reaction to compounds of similar chemical or biological composition to irinotecan, celecoxib, sulfonamides, or other study agents No active or ongoing infection No other concurrent uncontrolled illness No psychiatric illness or social situation that would preclude study compliance PRIOR CONCURRENT THERAPY: Biologic therapy No concurrent filgrastim (G-CSF) or sargramostim (GM-CSF) Chemotherapy See Disease Characteristics No more than 2 prior different chemotherapy regimens, including adjuvant therapy More than 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered No prior irinotecan Endocrine therapy Not specified Radiotherapy More than 4 weeks since prior radiotherapy and recovered No prior radiotherapy of more than 3,000 cGy No prior radiotherapy to extended marrow-generating fields No prior abdomino-pelvic irradiation Surgery No prior abdominoperineal resection Other More than 2 weeks since prior cyclo-oxygenase-2 (COX-2) inhibitors No concurrent combination antiretroviral therapy for HIV-positive patients No other concurrent investigational agents No other anticancer therapy No other concurrent COX-2 inhibitors Low-dose aspirin allowed