However, the same concerns CYP2D6 drug substrates from other therapeutic classes, e.g., tamoxifen, where Thorén et al. (2020) reported a significantly stronger impact of CYP2D6*41 than CYP2D6*10 on the CYP2D6-mediated bioactivation to endoxifen (Thorén et al., 2020), which mainly mediates the preventive effect on breast cancer recurrence. Here, CYP2D6 is linked to breast carcinoma.