PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: More than 12 weeks Hematopoietic: Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 10 g/dL Hepatic: Bilirubin less than 1.5 times upper limit of normal (ULN) SGOT/SGPT less than 2.5 times ULN Alkaline phosphatase less than 2 times ULN Renal: BUN less than 1.5 times ULN Creatinine less than 1.5 times ULN Other: Neurologically stable No nonmalignant systemic disease No acute infection treated with intravenous antibiotics No frequent vomiting No medical condition (e.g., partial bowel obstruction) that would interfere with oral medication intake No other prior or concurrent malignancy except surgically cured carcinoma in situ of the cervix or basal cell or squamous cell carcinoma of the skin No AIDS-related illness HIV negative Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception