To the Editor: Dr Schroth and colleagues1 described differences in efficacy of adjuvant tamoxifen on breast cancer outcome by an individual's CYP2D6 status. This 2-cohort study (609 extensive metabolizers and 716 decreased metabolizers) included prospectively collected data from 212 patients (enrolled 1991-1995)2 and retrospectively collected data from 1113 German patients (apparently 138 diagnosed before 20003 and 975 diagnosed after 2000).
Dieudonné A, Van Belle V, Neven P. Association Between CYP2D6 Polymorphisms and Breast Cancer Outcomes. JAMA. 2010;303(6):516-517. doi:10.1001/jama.2010.93