Abstract: The present invention relates to methods, compositions and kits related to a novel in vitro assay for a high-capacity and high-throughput method for measuring the ability of cancer cells to migrate in a three-dimensional cellular assay. The three-dimensional cellular invasion assay provides a method for determining and quantitating the metastatic potential and invasive capacity of a cancer cell. Other aspects of the invention further relate to the use of the in vitro assay to screen for agents and compounds capable of inhibiting intravasation, and thereby modulating the metastatic potential of cancer cells. The methods, compositions and three-dimensional assay provide a highly sensitive assay system capable of mimicking the in vivo cellular and molecular interactions required for successful completion of intravasation.