In the adjusted cox regression analyses encoding the predicted CYP2D6 activity as a continuous variable, CYP2D6 activity had no statistically significant influence on either breast cancer recurrence (adjusted HR [aHR] 1.18, 95% CI 0.92; 1.52) or breast cancer mortality (aHR 1.41, CI 0.93; 2.13) in the whole study cohort of patients who initiated tamoxifen as part of their adjuvant treatment. The gene discussed is CYP2D6; the disease is breast carcinoma.