Sustained lower rates of HRT prescribing and breast cancer incidence in Australia since 2003

Abstract

We previously reported a 6.7% drop in breast cancer incidence rates from 2001 to 2003 in women aged C50 years in Australia, and no significant change in incidence in women younger than 50 years [1]. This was in the context of a substantial and rapid fall of 40% in hormone replacement therapy (HRT) prescribing over the same period. We report here on the results of an updated analysis using national statistics on HRT prescribing and on breast cancer in Australia up to 2005. We used the same data sources and methods as previously described [1]. Figure 1 shows that the total number of HRT prescriptions in Australia remained low after 2003, with an overall 55% drop in prescribing occurring between 2001 and 2005. Figure 1 also shows that breast cancer incidence rates in women C50 years have remained at a sustained lower level in 2003–2005 compared to 2001. The incidence rates in this age group were lower by 8.8% (95% CI: 6.1–11.4%; P \ 0.0001) in 2005 compared to 2001, equivalent to 790 (95% CI: 550–1,020) fewer breast cancers (out of about 9,000 incident breast cancers for women of this age). Over the same period, there was no change in incidence in women aged 20–49 years (non-significant increase of 4.5%; P = 0.07). Rates for women\50 years in Fig. 1 are slightly higher than previously reported because of different weightings of the population at risk. The changes in breast cancer incidence in women aged C50 years occurred at a time of largely stable screening mammography rates in Australia. Age-standardised biennial breast cancer screening participation rates for Australian women aged 50–69 years were 56.9% in 2000–2001, slightly decreasing to 56.2% in 2002–2003 and thereafter remaining unchanged at 56.2% in 2004–2005 [2]. The trends in breast cancer incidence in Australia are strikingly similar to those reported in the USA [3, 4]. In both countries a rapid fall in use of HRT after 2001 was followed by a substantial drop in breast cancer rates in women aged C50 years between 2001 and 2003, with sustained lower rates observed after 2003. Declining trends in both HRT use and breast cancer incidence have now been reported in many countries [5] and are consistent with evidence from studies in individuals that the HRT-associated risk of breast cancer is reversible soon after ceasing use of HRT [6, 7, 8]. K. Canfell (&) Y. J. Kang A. Moa Cancer Epidemiology Research Unit, Cancer Council NSW, 153 Dowling Street, Woolloomooloo, Sydney, NSW, Australia e-mail: karenc@nswcc.org.au