The medical community has been debating for many years whether, and to what extent, postmenopausal hormone therapy (HT) use is associated with a higher risk of breast cancer, says Professor Amos Pines, President of the International Menopause Society. Although it is agreed that long-term HT slightly increases that risk, the definition of long-term use is still unclear, particularly in view of data showing that it may vary significantly by type of HT (estrogen-alone vs. estrogenprogestin, brand of progestin, dosage). A new study from the Kaiser Permanente health plan raises the question whether trends in breast cancer incidence and use of HT over the past 25 years may be directly linked.
The Womens Health Initiative (WHI) trial was a landmark in menopause medicine since it provided information based on the best available study methodology. By adopting its results as the ultimate source of information, many organizations, medical societies and health authorities actually declared that data derived from observations in the postmenopausal population are less valuable. Nevertheless, during the past few months, several studies have used databases on the incidence of breast cancer, on the one hand, and sales of HT on the other hand, in order to suggest a direct link between trends of hormone use and the number of newly diagnosed breast cancer patients. While such information, by itself, is very important and interesting, conclusions must be drawn with great caution. It is tempting to simplify the observed year-by-year figures on HT use and breast cancer incidence and establish a mirror glass equation: the more postmenopausal hormone use, the more breast cancer, and vice versa. But human biology is far too complicated and the pathophysiology of breast cancer is far too complex to adopt such a mechanistic approach, as the authors of those studies and related Editorials rightly say.