DISEASE CHARACTERISTICS: Histologically confirmed small cell lung cancer for which no potentially curative therapy exists Confirmation at relapse required only if sole relapse site is within previous radiation port No mixed histology Bidimensionally measurable disease by CT scan At least 1 measurable lesion at least 2 cm At least a partial response to front line chemotherapy Single regimen or alternating regimen allowed No initial course exceeding 8 courses or lasting more than 6 months No uncontrolled, untreated brain metastases No extensive liver metastases such that greater than 50% of liver parenchyma is replaced with metastatic disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0 or 1 Life expectancy: Not specified Hematopoietic: Absolute neutrophil count greater than 1,500/mm3 Platelet count greater than 100,000/mm3 Hepatic: Bilirubin normal SGOT/SGPT no greater than 2.5 times upper limit of normal (ULN) (5 times ULN if documented liver metastases) Renal: Creatinine less than 2.5 mg/dL Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 3 months after study Adequate unassisted oral or adequate enteral intake to maintain reasonable state of nutrition No other concurrent medical condition that would preclude study therapy

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior bone marrow transplantation No concurrent immunotherapy No concurrent myeloid colony stimulating factors (e.g., filgrastim (G-CSF), sargramostim (GM-CSF), interleukin-11) Chemotherapy: See Disease Characteristics At least 3 months since prior chemotherapy measured from day 1 of last course of front line therapy No prior high dose chemotherapy with marrow or stem cell rescue No more than 1 prior chemotherapy regimen No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy Radiotherapy: At least 2 weeks since prior radiotherapy No prior extensive radiotherapy (greater than 25% of bone marrow) No concurrent radiotherapy except for patients who are responding and develop brain metastases Surgery: Not specified Other: At least 30 days since prior investigational drugs No concurrent participation in another investigational trial No other concurrent experimental agents No other concurrent anticancer therapy No prophylactic oral or IV antibiotics for neutropenia