OUTLINE: This is a randomized, double blind, placebo controlled study. Patients are stratified by the number of involved disease sites at study entry, prior chemotherapy for metastases, osseous disease only at study entry, and bisphosphonate therapy at study entry, and concurrent hormonal therapy (yes vs no). Patients are randomized into two groups. Patients take either marimastat or placebo, one capsule orally twice a day, approximately every 12 hours (i.e., during or after breakfast and dinner). The drug or placebo is given until the development of progressive disease or prohibitive toxicity.