Breast Cancer Trends: A Marriage Between Clinical Trial Evidence and Epidemiology

In this issue of the Journal, Glass et al. (1) report on the changes in screening mammography, menopausal hormone therapy, and breast cancer incidence between 1980 and 2006 in the Kaiser Permanente Northwest (KPNW) health plan. In particular, they report a drop in breast cancer incidence between 2000 and 2004. Similar drops have been reported in other population-based studies (2,3). Considering the various interventions and practices employed by plan participants, the authors conclude that the patterns of screening mammography and menopausal hormone therapy "parallel" breast cancer incidence. They stop short of saying that either screening mammography or decreased menopausal hormone therapy use caused the drop in incidence between 2000 and 2004. But the paralleling implicates the latter.