The present invention relates to novel methods and compositions for detection and isolation of cancer cells with metastatic potential. The invention further relates to assays for measuring the metastatic potential of such cancer cells and drug screening assays for the identification of agents having anti-metastatic potential. The present invention further provides methods and compositions for inhibiting the metastatic potential of cancer cells by modulating the activity of serine integral membrane proteases [(SIMP) consisting of seprase and dipetidyl peptidase IV (DPPIV)] expressed on the surface of metastasizing cancer cells.