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