FAK (Focal Adhesion Kinase or PTK2) is a focal adhesion-associated protein kinase involved in cellular adhesion and spreading processes. It has been shown that when FAK was blocked, breast cancer cells became less metastatic due to decreased mobility. FAK is found concentrated in the focal adhesions that form among cells attaching to extracellular matrix constituents. FAK is a member of the FAK subfamily of protein tyrosine kinases that included PYK2 but lacks significant sequence similarity to kinases from other subfamilies. With the exception of certain types of blood cells, most cells express FAK. FAK tyrosine kinase activity can be activated, which plays a key important early step in cell migration. FAK activity elicits intracellular signal transduction pathways that promote the turn-over of cell contacts with the extracellular matrix, promoting cell migration.