In contrast, tamoxifen, which is widely used in endocrine therapy for ER-positive (luminal A and B) BCs, was shown to inhibit NK-mediated BC cell death by inducing the expression of the granzyme B inhibitor (serpentinB9/proteinase inhibitor 9), making these cells less responsive to NK despite the high expression of NK-activating ligands on their surface [153]. This evidence concerns the gene ESR1 and breast cancer.