PRIOR CONCURRENT THERAPY: Biologic therapy: Concurrent epoetin alfa allowed Chemotherapy: No prior systemic cytotoxic chemotherapy for malignant mesothelioma Prior intrapleural cytotoxic or sclerosing agents (including bleomycin) allowed No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy except the following: Steroids administered for adrenal failure Hormonal therapy administered for nonmalignant conditions (e.g., insulin for diabetes) Intermittent use of dexamethasone as an antiemetic Radiotherapy: At least 4 weeks since prior radiotherapy Prior irradiation of symptomatic lesion allowed if there is other measurable disease outside the radiation port No concurrent radiotherapy Surgery: At least 2 weeks since prior major surgery Other: No concurrent leucovorin calcium or folinic acid