Relationship between CYP2D6 genotype, tamoxifen metabolites, and adverse events, tumor biomarkers and breast cancer recurrence in a low-dose phase III trial in noninvasive disease.

1553Background: Low dose tamoxifen (T, 5 mg/d) given for 3 years halved recurrence in 500 women with non-invasive disease (DeCensi et al. JCO 2019). Retrospective studies with 20 mg/d have shown an...