DISEASE CHARACTERISTICS: Histologically confirmed small cell carcinoma Any primary site or unknown primary site Extensive or metastatic disease Lung primaries must have at least one of the following: Contralateral hilar adenopathy Contralateral supraclavicular adenopathy Malignant pleural effusion Distant metastases No brain metastases or CNS involvement Stable or responding disease to prior standard therapy allowed Measurable or evaluable disease prior to standard therapy