DISEASE CHARACTERISTICS:

• Histologically confirmed advanced solid tumor that is refractory to standard therapy OR
• Histologically confirmed chemotherapy-naive advanced cancer for which no curative therapy or higher priority palliative chemotherapy exists
• Brain metastasis allowed
• No bone marrow involvement of tumor

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 AND/OR
• Platelet count greater than 100,000/mm^3

Hepatic:

• ALT or AST less than 3 times upper limit of normal (ULN) (5 times ULN if liver metastases present)
• No autoimmune hepatitis

Renal:

• Creatinine less than 2.5 times ULN

Cardiovascular:

• No severe coronary artery disease
• No congestive heart failure

Pulmonary:

• No severe chronic obstructive pulmonary disease

Gastrointestinal:

• No frequent vomiting
• No medical condition that would interfere with oral medication intake (e.g., partial bowel obstruction, partial intestinal bypass, or external biliary diversion)

Other:

• No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix
• No known or suspected hypersensitivity to imidazotetrazin, interferon alfa, or any excipient or vehicle included in the formulation or delivery system of study drug
• No history of autoimmune disease
• No preexisting severe psychiatric condition or history of severe psychiatric disorder (including suicidal ideation or attempt)
• No life-threatening condition or severe preexisting condition
• No uncontrolled thyroid abnormalities
• No nonmalignant systemic disease
• No active uncontrolled infection
• HIV negative
• No AIDS-related illness
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 3 weeks since prior biologic agents (e.g., bi-specific antibodies, interleukin-2, or interferon) and recovered (excluding alopecia)
• No prior allogeneic, syngeneic, or autologous bone marrow or stem cell transplantation
• No other concurrent biologic therapy
• No concurrent colony stimulating factors or epoetin alfa for the prevention of myelotoxicity

Chemotherapy:

• See Disease Characteristics
• At least 4 weeks since prior chemotherapy (more than 6 weeks for nitrosoureas, melphalan, or mitomycin) and recovered (excluding alopecia)
• No prior high-dose chemotherapy and stem cell transplantation
• No more than 3 prior chemotherapy regimens
• No other concurrent chemotherapy

Endocrine therapy:

• Not specified

Radiotherapy:

• At least 6 weeks since prior wide-field radiotherapy to at least 25% of bone marrow (e.g., pelvic radiotherapy)
• More than 6 weeks since prior strontium chloride Sr 89 or samarium Sm 153 lexidronam pentasodium
• Recovered from prior radiotherapy (excluding alopecia)
• No concurrent radiotherapy

Surgery:

• At least 4 weeks since prior major surgery
• At least 1 week since prior minor surgery

Other:

• At least 4 weeks since prior investigational therapy