DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed solid tumor not amenable to standard therapy
• No symptomatic brain or leptomeningeal involvement

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• WHO 0-2

Life expectancy:

• At least 3 months

Hematopoietic:

• WBC at least 4,000/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin less than 1.5 mg/dL
• Other liver function tests no greater than 2 times upper limit of normal (unless related to liver metastases)

Renal:

• Creatinine no greater than 1.4 mg/dL

Other:

• Not pregnant or nursing
• Fertile patients must use effective contraception
• No active bacterial infection
• No other nonmalignant disease
• No alcoholism, drug addiction, or psychiatric disorders
• Able to take oral medication

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 4 weeks since prior immunotherapy

Chemotherapy:

• At least 4 weeks since prior chemotherapy (6 weeks since nitrosoureas)
• No other concurrent chemotherapy

Endocrine therapy:

• Not specified

Radiotherapy:

• At least 4 weeks since prior radiotherapy (6 weeks since extensive radiotherapy)
• No concurrent radiotherapy (except palliative radiotherapy)

Surgery:

• Not specified

Other:

• No other concurrent investigational drugs
• No other concurrent antitumor drugs