NCAM1 and breast cancer: However, even if the NK-activating ligand, CD72, whose corresponding receptor (SEMA4D) is expressed by NK-92 cells (Supplementary Fig. 5B) might play a role in inducing breast cancer sensitivity to NK-mediated cytotoxicity (a hypothesis that needs to be tested), the role of CD56 in this same mentioned process is independent of the expression CD72.