RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug may kill more tumor cells. It is not yet known whether three courses of combination chemotherapy are more effective than six courses of combination chemotherapy for non-small cell lung cancer.

PURPOSE: Randomized phase III trial to compare the effectiveness of three courses of combination chemotherapy with that of six courses of combination chemotherapy in treating patients who have stage IIIB or stage IV non-small cell lung cancer.

OBJECTIVES: I. Compare the duration of symptom control, time to disease progression, survival, and quality of life in patients with stage IIIB or IV non-small cell lung cancer treated with 3 versus 6 courses of mitomycin, vinblastine, and cisplatin.

OUTLINE: This is a randomized, multicenter study. Patients are stratified by stage of disease (stage IIIB vs IV). Patients are randomized to 1 of 2 treatment arms: Arm I: Patients receive cisplatin IV over 4 hours, mitomycin IV, and vinblastine IV on day 1. Treatment repeats every 3 weeks for 3 courses in the absence of disease progression or unacceptable toxicity. Mitomycin is not administered during course 3. Arm II: Patients receive chemotherapy as in arm I. Treatment repeats every 3 weeks for 6 courses in the absence of disease progression or unacceptable toxicity. Mitomycin is not administered during courses 3 and 5. Quality of life is assessed after completion of 3 courses of chemotherapy for patients in arm I and after completion of 4, 5, and 6 courses for those in arm II. Patients may receive radiotherapy beginning after completion of chemotherapy.

PROJECTED ACCRUAL: A total of 310 patients will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically proven stage IIIB or IV non-small cell lung cancer that is not eligible for surgery or radical radiotherapy

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Zubrod-WHO 0-2 Life expectancy: Not specified Hematopoietic: Hemoglobin greater than 10 g/dL WBC greater than 3,000/mm3 Platelet count greater than 100,000/mm3 Hepatic: Liver function tests no greater than 2 times normal (unless due to metastatic disease) Renal: Creatinine clearance greater than 60 mL/min EDTA clearance greater than 60 mL/min Other: No serious, uncontrolled, concurrent medical illness

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior conventional chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics Surgery: See Disease Characteristics