Retrovirus-mediated TIMP-2 gene transfer into human breast cancer cells is able to down-regulate invasion and show that tumor-derived angiogenesis is reduced. In this model, retroviral-mediated transduction of TIMP-2 cDNA into a limited population of human tumor cells inhibits tumor growth and prevents distant pulmonary metastasis. These results indicate that it may not be necessary to deliver and express these genes in every single tumor cell as long as the level of expression in a limited number of transduced cells is sufficient to prevent the excessive breakdown of the extracellular matrix.