CD9 and neoplasm: Future studies should aim to elucidate the mechanism by which PKCα regulates α3β1 function in tumor cells, and the interplay between CD9/CD81, CD151, and other TEM-resident proteins such as the major CD9/CD81 partners, IgSF proteins EWI-2 and EWI-F/CD9P-1, in regulating metastatic cell behaviors.