PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Zubrod 0-1 OR Karnofsky 80-100% Life expectancy: At least 12 weeks Hematopoietic: Absolute granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 8 g/dL Hepatic: Bilirubin no greater than 1.5 mg/dL No Gilbert's syndrome Renal: Creatinine no greater than 1.5 mg/dL Calcium no greater than 12 mg/dL OR No symptomatic hypercalcemia under treatment Cardiovascular: No New York Heart Association class III or IV heart disease No angina, myocardial infarction, or congestive heart failure within the past 6 months Gastrointestinal: No intestinal obstruction No diarrhea (greater than 4 loose stools per day) Able to swallow Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No concurrent serious infection or nonmalignant medical illness that is uncontrolled or for which control may be jeopardized by complications of study therapy No history of seizures No psychiatric disorder that would preclude compliance No other malignancy within the past 5 years except nonmelanomatous skin cancer or carcinoma in situ of the cervix No pre-existing cystitis