Irinotecan and Gemcitabine in Treating Patients With Recurrent or Progressive Stage III or Stage IV Non-Small Cell Lung Cancer

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed non-small cell lung cancer (NSCLC), meeting 1 of the following stage criteria: Stage IIIA or IIIB disease Progressive disease Stage IV disease Failed 1 prior platinum-based chemotherapy regimen, including adjuvant therapy Measurable or evaluable disease, as defined by 1 of the following criteria: At least 1 unidimensionally measurable lesion ≥ 20 mm by conventional techniques OR > 10 mm by spiral CT scan Lesions apparent on CT scan that do not meet the criterion for measurability Brain metastases allowed provided patient has received definitive therapy for metastases, is asymptomatic, and has extra-CNS metastases PATIENT CHARACTERISTICS: Age 18 and over Performance status ECOG 0-1 Life expectancy More than 12 weeks Hematopoietic WBC ≥ 3,000/mm^3 Absolute neutrophil count ≥ 1,500/mm^3 Platelet count ≥ 100,000/mm^3 Hepatic AST and ALT ≤ 1.5 times normal Alkaline phosphatase < 1.5 times normal Bilirubin ≤ 1.3 mg/dL Renal Creatinine ≤ 1.6 mg/dL OR Creatinine clearance ≥ 50 mL/min Cardiovascular No unstable angina No congestive heart failure No myocardial infarction within the past 3 months No life-threatening ventricular arrhythmia requiring maintenance therapy Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective barrier contraception during and for 3 months after completion of study treatment No uncontrolled seizure disorder No uncontrolled diabetes mellitus No active infection requiring systemic therapy No other malignancy within the past 5 years except nonmelanoma skin cancer or carcinoma in situ of the cervix No other unstable or serious condition PRIOR CONCURRENT THERAPY: Biologic therapy Not specified Chemotherapy See Disease Characteristics At least 3 weeks since prior chemotherapy Prior irinotecan allowed No prior gemcitabine No more than 1 prior chemotherapy regimen for NSCLC, excluding gefitinib No other concurrent chemotherapy Endocrine therapy Not specified Radiotherapy At least 4 weeks since prior radiotherapy No concurrent radiotherapy Surgery Not specified Other More than 1 month since prior participation in another clinical trial using an investigational agent No other concurrent investigational agents