DISEASE CHARACTERISTICS:

• Histologically confirmed metastatic or surgically unresectable solid tumor, having received the following maximum number of prior therapies for advanced disease:

  • Bladder cancer - no more than 1 prior therapy
  • Breast cancer - no more than 2 prior therapies
  • Colorectal cancer - no more than 1 prior therapy
  • Kidney cancer - no prior therapy
  • Lung cancer - no more than 1 prior therapy
  • Pancreatic cancer - no prior therapy

• Bidimensionally measurable disease outside a previously irradiated field

  • At least 2 cm x 2 cm
• No known bone metastases
• CNS involvement allowed if successfully controlled by surgery or radiotherapy and not requiring corticosteroids

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Menopausal status:

• Not specified

Performance status:

• ECOG 0-2

Life expectancy:

• At least 3 months

Hematopoietic:

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

Hepatic:

• Bilirubin no greater than 1.5 mg/dL regardless of liver involvement secondary to tumor
• SGOT no greater than 3 times upper limit of normal (ULN) (no greater than 5 times ULN if liver metastases present)
• No known Gilbert's disease

Renal:

• Creatinine no greater than 1.8 mg/dL
• Calcium less than 12.0 mg/dL

Cardiovascular:

• No myocardial infarction within the past 6 months
• No congestive heart failure requiring therapy

Other:

• No active uncontrolled bacterial, viral (including HIV), or invasive fungal infection
• No psychiatric disorders that would prevent compliance
• No other malignancy within the past 5 years except adequately treated basal or squamous cell skin cancer or carcinoma in situ of the cervix
• No history of seizures
• Not pregnant or nursing
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No concurrent sargramostim (GM-CSF)
• No concurrent immunotherapy

Chemotherapy:

• No prior irinotecan, topotecan, or gemcitabine
• Prior adjuvant chemotherapy allowed, if at least 1 year between last dose of adjuvant chemotherapy and recurrence of cancer
• No other concurrent chemotherapy

Endocrine therapy:

• Not specified

Radiotherapy:

• See Disease Characteristics
• At least 4 weeks since prior radiotherapy to less than 30% of bone marrow
• No prior whole pelvic radiotherapy
• No concurrent radiotherapy

Surgery:

• See Disease Characteristics

Other:

• No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis