The impact of menopausal hormone therapy on the incidence of different breast cancer types––Data from the Cancer Registry Hamburg 1991–2006

The publication of the Women's Health Initiative Study [1] in 2002 and the Million Women Study [31] in 2003 on the association of menopausal hormone therapy (HT) and breast cancer were followed by a decrease in the prescription of HT to menopausal women in western countries. In the following years several papers from different countries reported declines in breast cancer incidence and discuss whether this decline is related to the decreased use of menopausal hormone therapy. We contribute further data by analysing breast cancer incidence rates from the Hamburg Cancer Registry, Germany, for the time period 1991–2006 and HT use data from a large case–control study conducted in the Hamburg region. At first we determined whether there is a decline in breast cancer incidence in 2002/2003. To find supporting evidence for a causal relationship between breast cancer incidence and use of menopausal hormones we addressed the following issues: The decline in incidence should be more pronounced in the age groups, in which HT is used predominantly, i.e. age group 50–69. The decline in incidence should be most pronounced for breast cancer types more strongly associated with HT, i.e. invasive lobular cancer. We observed a statistical significant decline in incidence of all invasive breast cancer in 2002/2003 in Hamburg. The increase in breast cancer incidence as well as the decline was most pronounced in the age group 50–69. Regarding the histological types of tumours in this age group the decline was only pronounced for invasive lobular cancer. The estimated prevalence of HT indicates a decreasing hormone use starting in 2001/2002. We found a strong decrease in prescriptions for menopausal hormone therapy between 2002 and 2005. In summary, our data add to the evidence of a relation between breast cancer incidence and menopausal hormone use.