The data obtained from experimental groups of healthy and breast cancer patient donors indicated there was no obvious expression of perforin, granzyme B, and IFN-γ of NK cells in Group 1 (MDA-MB-231 breast cancer cell lines alone) and Group 2 (MDA-MB-231 breast cancer cell lines + MEPB); in contrast, there was an increased expression in Group 3 (MDA-MB-231 breast cancer cell lines + NK cells) and Group 4 (MDA-MB-231 breast cancer cell lines+NK cells+ MEPB). This evidence concerns the gene PRF1 and breast cancer.