PATIENT CHARACTERISTICS: Age: 18 to 70 Performance status: WHO 0-2 Life expectancy: Not specified Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) AST or ALT less than 2.5 times ULN Alkaline phosphatase less than 2.5 times ULN No chronic hepatitis B or C Renal: Creatinine no greater than 1.5 times ULN Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No known HIV infection No medical condition that would interfere with oral medication intake (e.g., frequent vomiting or partial bowel obstruction) No other prior or concurrent malignancy except surgically cured carcinoma in situ of the cervix or nonmelanoma skin cancer No serious medical, psychological, familial, sociological, or geographical condition that would preclude study