Update of the evolution of breast cancer incidence in relation to hormone replacement therapy use in Belgium

Background: Several studies reported a decrease in breast cancer (BC) incidence, subsequent to the decrease in hormone replacement therapy (HRT) use.

Aim: Although Belgium has one of the highest incidences of BC in Europe and one of the highest rates of HRT use, we were unable, in a previous study, to observe a significant association between BC incidence and HRT changes. In this updated report we added the BC data from incidence years 2007 and 2008.

Material and method: We used European standardized incidence rates for invasive BC in the age class 50-69 years for Flanders (1999-2008), Brussels and Wallonia (2004-2008), obtained from IMS Health HRT sales data (1997-2008) for Brussels, Flanders and Wallonia. The association between BC incidence and HRT use was analyzed using generalized estimating equations (GEE) in order to take into consideration the dependency between the subsequent data points.

Results: There was a significant association between the invasive BC incidence rate and estimated rate of HRT users in the previous year: p-value<0.001.

Conclusion: Although this study is hampered by a number of limitations, these data support the idea that the drop in BC incidence can be partly attributed to the decrease in HRT use. Since HRT remains the most used medication for climacteric symptoms, we encourage the creation of a prospective registry in Europe, collecting detailed data in various European countries, in order to assess the adjusted increase in BC risk associated with HRT, which may be population and regimen dependent.