It has been discovered that IFN-γ has anti-tumoral effect as it manages to inhibit the growth of tumor cell lines including breast cancer cells by causing cell cycle arrest in the expense of p21 up-regulation as reported in previous studies [37] while in another findings, indicate that IFN-γ increases the growth inhibitory effect of tamoxifen in breast metastatic carcinomas [38]. This evidence concerns the gene IFNG and breast cancer.