Decline in breast cancer incidence after decrease in utilisation of hormone replacement therapy

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Abstract
Hormone replacement therapy (HRT) has been implicated as a risk factor for breast cancer and the use of HRT has decreased substantially in general population over the last years. Recently, there are first indications that breast cancer incidence has started declining. We examined recent breast cancer incidence and actual data on HRT utilisation in Schleswig-Holstein, Germany, to find out population based evidence on decreasing breast cancer incidence and its possible relationship with reduced HRT usage. Breast cancer incidence is taken from the population based cancer registry of Schleswig-Holstein. HRT data was extracted from a cohort of 102,000 women taking part in a quality assurance project in breast cancer diagnosis for the years 2001–2005. The annual percentage change in incidence of breast cancer and HRT utilisation was measured by linear regression. There is a linear decline in HRT utilisation among less than 50 years group, 50–69 years group and all age group women between the years 2001 and 2005. Breast cancer incidence decreased between the years 2001 and 2005 for more than 50 years old and all age group, but not in the younger than 50 years women. The decline of breast cancer incidence started about two years after the HRT decline. Breast cancer incidence decline and decreased HRT utilisation showed a high correlation. A drastic change in age-incidence relationship in breast cancer has taken place, the change is likely to continue and in future it has to be monitored closely with HRT use and other possible explanations.