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