Kruijf et al. [45] studied 677 breast cancer patients from 1985 to 1994 to verify the expression of NKG2D ligands (NKG2DL) using immunohistochemical staining and they found that NKG2DL was frequently expressed by tumors (ULBP1, 90% of the cases; ULBP2, 99%; ULBP3, 100%; ULBP4, 26%; ULBP5, 90%). This evidence concerns the gene KLRK1 and breast cancer.