OBJECTIVES: I. Determine whether treatment with the oral matrix metalloproteinase inhibitor (MMPI) marimastat prolongs overall survival and time to progression in patients with small cell lung cancer who have achieved complete or partial remission after first line chemotherapy, with or without radiotherapy. II. Determine the tolerability and toxicity of prolonged administration of marimastat in patients with small cell lung cancer. III. Determine the effect of prolonged administration of marimastat on the quality of life of patients with small cell lung cancer.