In breast carcinoma MCF-7 cells, CD99 may function as a negative regulator of FAK-mediated tumorigenesis and metastasis by recruiting the protein tyrosine phosphatase SHP2 which dephosphorylates FAK and blocks the positive pro-tumorigenic signaling of CD98/integrins/FAK/RhoA/ROCK [88]. Here, PTK2 is linked to breast carcinoma.