In spite of the progress that has been made in the last decade, cancer remains a major cause of human death. A novel anticancer therapy, based on the destruction of blood vessels within tumors, however offers new hope. It is derived from the principle that tumor cells, like healthy cells, require oxygen and nutrients to survive. This formation of blood vessels in tumors, a process called angiogenesis, is thus essential for tumor development and allows the formation of metastases. To discover effective means of blocking tumor-associated blood vessel formation, we need to understand the molecular events that underlie their formation. In this context, we have been studying an enzyme called DEP-1, which is part of a family of protein tyrosine phosphatases. The results we have obtained so far support a role for DEP-1 in the regulation of blood vessel formation. Therefore, our research goal is to demonstrate mechanistically how DEP-1 contributes to angiogenesis. The knowledge generated will lead to the development of novel strategies to block angiogenesis and tumor progression.