CYP2D6 and breast cancer: In a study conducted by Blancas et al. in 2018, a significantly lower disease-free survival was observed in a set of 87 patients taking adjuvant tamoxifen treatment with slow metabolisers compared to the rapid counterparts [73]; we refer the reader to in-depth reviews [74,75] of how the variant alleles of CYP2D6 can be used to predict the outcome in tamoxifen-treated breast cancer patients.