Our data in this context are in agreement with many published studies in literature which reported that Reduced CYP2D6 activity is usually associated with poor treatment outcomes, increased risk of recurrence and shortened recurrence as well as with overall free survival rates in breast cancer patients treated with Tamoxifen (Thota et al., 2018, Kiyotani et al., 2010). This evidence concerns the gene CYP2D6 and breast cancer.