Marimastat is a broad spectrum matrix metalloprotease (MMP) inhibitor. It is an angiogenesis and metastasis inhibitor. It mimics the peptide structure of natural MMP substrates and binds to matrix metalloproteases, thereby preventing the degradation of the basement membrane by these proteases. This antiprotease action prevents the migration of endothelial cells needed to form new blood vessels. Inhibition of MMPs also prevents the entry and exit of tumor cells into existing blood cells, thereby preventing metastasis. Marimastat has been in pivotal phase III trials in glioblastoma, breast, ovarian and small and non-small cell lung cancer, but these trials have all been discontinued because marimastat failed to show superior efficacy over either standard chemotherapy or placebo.