DISEASE CHARACTERISTICS:

• Histologically confirmed colorectal carcinoma

  • Stage II (T3-4, N0, M0) or stage III (any T, N1-2, M0) disease
• Completely resected primary tumor without gross or microscopic evidence of residual disease

• Must have received potentially curative therapy within the past 12 weeks, including any of the following:

  • Surgery alone
  • Surgery plus radiotherapy and/or chemotherapy

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• WHO 0-1

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• AST/ALT no greater than 1.5 times ULN

Renal:

• Creatinine clearance greater than 30 mL/min

Cardiovascular:

• No severe congestive heart failure

Other:

• Not pregnant or nursing
• Fertile patients must use effective contraception
• No active peptic ulcer or gastrointestinal bleeding within the past year
• No inflammatory bowel disease
• No known sensitivity to rofecoxib
• No prior adverse reaction to non-steroidal anti-inflammatory drugs (NSAIDs) (e.g., asthma, acute rhinitis, nasal polyps, angioneurotic edema, or urticaria)
• No other malignancy within the past 10 years except adequately treated carcinoma in situ of the cervix or basal cell or squamous cell skin cancer

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• See Disease Characteristics

Endocrine therapy:

• Not specified

Radiotherapy:

• See Disease Characteristics

Surgery:

• See Disease Characteristics

Other:

• No concurrent long-term NSAIDs except low-dose aspirin (no more than 80 mg/day) for cardio-prophylaxis