Reduced risk of oestrogen receptor positive breast cancer among peri- and post-menopausal women in Scotland following a striking decrease in use of hormone replacement therapy.

Many countries report a decline in breast cancer incidence among peri- and post-menopausal women following a decline in HRT prescribing. To investigate recent Scottish incidence trends, European age-standardised incidence rates from 1997 to 2005 were stratified by method of first detection, ER status and age group. We developed change point models of the annual age-specific cases for the peri- and post-menopausal age groups and ER status using Poisson regression. In Scotland all HRT categories together show a 32.4% increase in the number of items dispensed in 1993-2000 followed by a striking 61.8% decline by 2007. The incidence rates of screen-detected tumours increased gradually in the 50-64 and 65-74 age groups. For the older age group this increase accelerated after 2003 corresponding to an extension of the age range of screening. For ER positive tumours in the 50-64 age group, age-standardised rates increased 31.5% from 1997 to 2000, followed by a statistically significant decrease of 11.2% by 2005 (change in slope=-0.0943, P<0.0001). We conclude that an overall incidence in the 50-64 age group declined since 2000 reflecting the sudden fall in HRT dispensed items and is largely accounted for by the decrease in ER positive tumour incidence. A longer term decline in ER negative tumours for this age group was pre-existing and is unaffected by the collapse in HRT prescribing.