Based on the still considerable controversy over the relationship between CYP2D6 genotype and/or endoxifen concentrations and clinical outcome, our theoretical in silico simulation work suggests as next step the investigation of our proposed MIPD framework in comparison to the conventional ‘one-dose-fits-all’ dosing strategy in a well-designed and -powered prospective clinical trial setting, allowing to evaluate the ‘real-world’ clinical benefit (i.e., the possibility of achieving recduced breast cancer recurrence rates) and (long-term) safety of MIPD for tamoxifen. This evidence concerns the gene CYP2D6 and breast cancer.