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

Abstract

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.