Although further research is needed to define the exact mechanisms, in vitro and in vivo models evidenced that ALCAM participates in cell-cell adhesion and collective cell migration, and suggested that to allow invasion in the frontier between tissues-restricted carcinoma and disseminated tumor cells, a dynamic and adaptive switch between ALCAM expression at the cell surface and cleaved ALCAM by MMP-9 might take place. This evidence concerns the gene MMP9 and neoplasm.