Combination Chemotherapy in Treating Patients With Recurrent or Refractory Small Cell Lung Cancer

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