MMP9 and cancer: In particular, MMP-9 is pivotal in all steps of the metastatic process, in that it strongly contributes to the ability that cancer cells have to: (1) disrupt the cell-to-cell or cell-to-ECM interactions that maintain the primary tumor mass; (2) penetrate local ECM and vessels; (3) exit the vessel and migrate into the extravascular space; and (4) survive and proliferate in foreign tissue [1,3,10,11].