The rise and fall in menopausal hormone therapy and breast cancer incidence

Studies conducted in different areas of North America and Europe showed a 5–10% decline in the incidence of breast cancer following reductions up to 70% in menopause hormone therapy (HT) use after 2002. The observation that the decline was larger in (or limited to) women aged ≥50 years weighs in favour of an effect of reduced HT use on breast cancer incidence. However, changes in screening are also likely to play a role in the decreasing incidence of breast cancer observed in several countries. In particular, the technical improvements and the increased effectiveness of breast cancer screening and detection during the 1990s led to a decreased number of pre-clinical cases found by screening in subsequent years. Further, disentangling the effects of HT use and screening is difficult, as women who stop using HT may also undergo mammography screening less frequently. Thus, the reasons of the falls in incidence remain open to discussion.