DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed adenocarcinoma of the colon or rectum

  • Locally advanced, locally recurrent, or metastatic disease
  • Not curable by surgery and/or not amenable to radiotherapy with curative intent
  • Histological or cytological confirmation of metastatic cancer not required for patients with prior surgically resected colorectal cancer if more than 5 years elapsed between primary surgery and development of metastatic disease OR if primary cancer was stage I or II
• Prior adjuvant therapy with fluorouracil or immunotherapy for resected stage II, III, or IV disease allowed
• Measurable disease
• No known brain metastases

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-1

Life expectancy:

• More than 12 weeks

Hematopoietic:

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

Hepatic:

• Bilirubin normal
• AST/ALT no greater than 5 times upper limit of normal

Renal:

• Creatinine normal

Cardiovascular:

• No uncontrolled high blood pressure
• No unstable angina
• No symptomatic congestive heart failure
• No myocardial infarction within the past 6 months
• No serious uncontrolled cardiac arrhythmia
• No New York Heart Association class III or IV heart disease

Other:

• No active or uncontrolled infection
• No predisposing colonic or small bowel disorders with uncontrolled symptoms as indicated by more than 3 loose stools daily in patients without a colostomy or ileostomy
• No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or adequately treated noninvasive carcinomas
• No other concurrent medical or psychiatric condition that would preclude study
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• See Disease Characteristics
• At least 12 months since prior immunotherapy

Chemotherapy:

• See Disease Characteristics
• At least 12 months since prior fluorouracil
• No prior chemotherapy for advanced colorectal cancer
• No prior irinotecan

Endocrine therapy:

• Not specified

Radiotherapy:

• See Disease Characteristics
• No prior radiotherapy to more than 15% of bone marrow
• At least 4 weeks since prior major radiotherapy (e.g., chest or bone palliative radiotherapy)
• No concurrent radiotherapy

Surgery:

• See Disease Characteristics
• At least 4 weeks since prior major surgery (e.g., laparotomy) and recovered
• At least 2 weeks since prior minor surgery and recovered
• No concurrent ophthalmic surgery

Other:

• No prior ZD 1839
• No other concurrent investigational or commercial agents or therapies for malignancy
• No concurrent combination antiretroviral therapy for HIV
• No concurrent oral retinoids
• No concurrent prochlorperazine on day of irinotecan administration