OUTLINE: This is a randomized, double blind, multicenter, placebo controlled study. Patients are stratified by stage of disease at diagnosis, response to prior chemotherapy/radiotherapy, type of thoracic radiotherapy, and cooperative group. Patients are randomized into two groups. Half of the patients take marimastat orally twice a day (breakfast and evening meal); the other half take placebo orally twice a day (breakfast and evening meal). Treatment continues for 2 years or until documented disease recurrence or progression and institution of further anticancer treatment, occurrence of unacceptable toxicity, initiation of anticoagulant treatment, or development of intercurrent illness. All patients are followed every 6 months until death.