Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed relapsed or progressive small cell lung
cancer

- Classical or intermediate variant OR

- Relapsed or progressive extrapulmonary small cell carcinoma of unknown origin

- Bidimensionally measurable disease

- At least 1 cm by 1 cm by physical exam or radiologic exam

- Outside prior radiation port unless clinical evidence of disease progression

- Previously radiated brain metastases allowed provided stable or improved

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Performance status:

- ECOG 0-2

Life expectancy:

- More than 12 weeks

Hematopoietic:

- Absolute neutrophil count at least 1,500/mm3

- Platelet count at least 100,000/mm3

Hepatic:

- Bilirubin no greater than 2 times upper limit of normal (ULN)

- SGOT/SGPT no greater than 3 times ULN (5 times ULN if liver metastases present)

- Alkaline phosphatase no greater than 5 times ULN

Renal:

- Creatinine no greater than 2 mg/dL

Other:

- HIV negative

- No AIDS-related illness

- No frequent vomiting or medical condition that would interfere with oral medication
administration (e.g., partial bowel obstruction)

- No active nonmalignant systemic disease that would preclude study

- No other active invasive malignancy within the past year or concurrently requiring
ongoing treatment

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception for at least 1 month before,
during, and for at least 3 months after study

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- At least 4 weeks since prior biologic therapy

- No concurrent immunotherapy

- No concurrent biologic therapy

- Concurrent epoetin alfa allowed

Chemotherapy:

- At least 4 weeks since prior chemotherapy

- No more than 1 prior continuous or discontinuous chemotherapy regimen for metastatic
disease

- No other concurrent chemotherapy

Endocrine therapy:

- Concurrent hormonal therapy to boost appetite allowed (e.g., corticosteroids or
medroxyprogesterone)

Radiotherapy:

- See Disease Characteristics

- At least 4 weeks since prior radiotherapy to 15% or more of bone marrow

- At least 1 week since prior radiotherapy to less than 15% of bone marrow

- No prior radiotherapy to 50% or more of bone marrow

- No concurrent radiotherapy

Surgery:

- Not specified

Other:

- Recovered from prior therapy

- No other concurrent investigational drugs

- Concurrent pamidronate allowed