Commentary: Hormone therapy and breast cancer incidence: did epidemiologists miss an effect on national trends?

Publication of the Women’s Health Initiative trial of post-menopausal hormone therapy caused re-thinking and heart-searching in epidemiology,1 although the scale of the upset at that time can be exaggerated. As Krieger and colleagues have pointed out elsewhere, biological, clinical and epidemiological evidence ques-tioning the purported benefits of hormone therapy on heart disease and counting the harms had been available well before 2002.2 Krieger in this volume has turned to the effects of hormone therapy on breast cancer risk and asks an important question: if the effect of hormone therapy on breast cancer was established from the 1970s, why was so little attention paid to the effects of hormone therapy on national breast cancer rates?3 Breas