Irinotecan and Carboplatin in Treating Patients With Metastatic or Recurrent Small Cell Lung Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed small cell lung cancer, meeting 1 of the following criteria: * Previously untreated metastatic or extensive disease * Malignant pleural effusion or multifocal lung disease is considered metastatic or extensive disease * Prior radiotherapy allowed * Recurrent disease * Limited, metastatic, or extensive disease * Relapsed after prior chemotherapy, excluding irinotecan hydrochloride * At least 90 days since prior chemotherapy * Measurable disease, defined as ≥ 1 unidimensionally measurable lesion ≥ 1 cm by physical examination or radiographic techniques * Known brain metastases allowed PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Life expectancy ≥ 3 months * White Blood Cells \> 3,000/mm³ * Absolute neutrophil count ≥ 1,500/mm³ * Platelet count ≥ 100,000/mm³ * Hemoglobin ≥ 9.0 g/dL * Bilirubin ≤ 1.5 mg/dL * SGOT ≤ 2.5 times upper limit of normal (ULN) (5 times ULN if liver metastases present) * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 3 months after completion of study treatment * No medical disease that, in the opinion of the investigator, would preclude study treatment PRIOR CONCURRENT THERAPY: * See Disease Characteristics * At least 10 days since prior radiotherapy (including brain) * No prior irinotecan hydrochloride * At least 2 weeks since prior and no concurrent anticonvulsants * No concurrent radiotherapy