DISEASE CHARACTERISTICS:

• Pathologically proven advanced cancer for which no curative therapy exists

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-2

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count greater than 1,500/mm^3
• Platelet count greater than 100,000/mm^3
• Hemoglobin greater than 9 g/dL

Hepatic:

• Bilirubin normal
• SGOT and SGPT no greater than 2 times upper limit of normal (ULN) (no greater than 5 times ULN if liver metastases present)

Renal:

• Creatinine normal

Other:

• Unassisted oral or enteral intake sufficient to maintain a reasonable state of nutrition
• No concurrent medical condition that is likely to interfere with study participation
• No active visual disturbances that require intervention beyond corrective lenses
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No prior bone marrow transplantation
• No concurrent immunotherapy

Chemotherapy:

• At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin)
• No prior high dose chemotherapy with bone marrow or stem cell rescue
• No other concurrent chemotherapy

Endocrine therapy:

• No concurrent hormone therapy (except megestrol acetate)

Radiotherapy:

• At least 4 weeks since prior radiotherapy
• No prior radiotherapy to 25% or more of bone marrow
• No concurrent radiotherapy (except palliative radiotherapy within the first 28 days of the study)

Surgery:

• Not specified

Other:

• At least 30 days since prior investigational therapy
• No concurrent investigational therapy