RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug may kill more tumor cells.

PURPOSE: Phase II trial to study the effectiveness of combination chemotherapy in treating patients who have recurrent or refractory small cell lung cancer.

OBJECTIVES: I. Determine the overall, complete, and partial response rates of patients with recurrent or refractory small cell lung cancer when treated with gemcitabine plus irinotecan. II. Determine the overall and failure free survival of these patients when treated with this regimen. III. Determine the duration of response of these patients after this treatment. IV. Evaluate the toxicity associated with the administration of this treatment in this patient population.

OUTLINE: Patients are stratified according to prior response duration (progression 90 days or more after initial therapy vs progression less than 90 days after initial therapy or no response to initial therapy). Patients receive gemcitabine IV over 30 minutes and irinotecan IV over 90 minutes on days 1 and 8. Treatment continues every 21 days in the absence of disease progression or unacceptable toxicity. Patients are followed every 3 months for 1 year, then every 6 months for 2 years, and then annually for 3 years.

PROJECTED ACCRUAL: A total of 78 patients will be accrued for this study over 12-18 months.

• Drug: gemcitabine hydrochloride
• Drug: irinotecan hydrochloride

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed recurrent or refractory small cell lung cancer Measurable disease At least 20 mm with conventional techniques OR At least 10 mm with spiral CT scan The following are not considered measurable: Bone lesions Leptomeningeal disease Ascites Pleural/pericardial effusion Abdominal masses not confirmed and followed by imaging techniques Cystic lesions Tumor lesions situated in a previously irradiated area Known CNS metastases allowed

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: CTC 0-2 Life expectancy: Not specified Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL Renal: Creatinine no greater than 2.0 mg/dL Other: Not pregnant or nursing Fertile patients must use effective contraception No prior or concurrent malignancy in past 5 years except curatively treated carcinoma in situ of the cervix, breast, or basal cell or squamous cell carcinoma of the skin

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 1 prior chemotherapy or chemoradiotherapy regimen No prior gemcitabine or irinotecan Endocrine therapy: Not specified Radiotherapy: No more than 1 prior chemoradiotherapy regimen At least 2 weeks since prior cranial radiotherapy for CNS metastases No concurrent cranial radiotherapy Surgery: Not specified