Tamoxifen, CYP2D6 and endoxifen in the treatment of hormone sensitive breast cancer: demystifying the connections

The role of the selective oestrogen receptor modulator, tamoxifen, is well established in the treatment of hormone sensitive breast cancer. The metabolism of tamoxifen to its active metabolites is however complex. Despite much research, a conclusive stance on the clinical implications of CYP2D6, active metabolites including endoxifen in efficacy and toxicity, is yet to be reached. Herein we examine the literature to clarify the connections between tamoxifen, CYP2D6 and endoxifen with resultant clinical recommendations.