Breast cancer incidence and use of hormone therapy in Denmark 1978-2007

Internationally, there have recently been reports of declining incidence rates for breast cancer. Decreased use of hormone therapy and decreased use of mammography has been put forward as possible reasons for this decline. The aim of this study was to analyse breast cancer incidence trends in Denmark, and to evaluate if these trends could be explained by changes in use of hormone therapy and screening with mammography. Data was obtained from the Danish Cancer Register, the Danish Medicines Agency, the Danish National Board of Health and the organised screening programmes. Incidence had been decreasing since 2003 with an annual percent change (APC) of -0.40. The proportion of women treated with hormone therapy dropped from 11.9% in 2002 to 8.8% in 2008, with a 67% drop in the use of oestrogens and progestogens combined, during the same period. Danish data show a slight decease in the incidence, and while showing a significant drop in hormone therapy use, these results are coherent with a comparatively low initial use of hormone therapy. Mammography use increased over the period, and hence does not explain the decrease in incidence, but might have caused an underestimate of the effect of decreased use of hormone therapy.