Breast cancer cases fell as HRT use dropped: study

Breast cancer rates fell as women turned away from hormone replacement therapy, a study has shown, boosting understanding of how the two are linked.

Breast cancer rates fell as women in Canada shunned hormone replacement therapy, research has found. Photo: CORBIS

Use of HRT to combat the effects of the menopause halved in Britain after studies suggested it could increase the risk of breast cancer.

A study conducted in Canada has now found that as use of the treatment dropped, the number of cases of breast cancer detected also reduced.

However after several years breast cancer rates began to increase again which, researchers said, suggests that not using HRT simply led to their tumours growing more slowly.

The hormone, oestrogen, contained in some forms of HRT can fuel certain types of breast cancer.

So the research suggests that the link between breast cancer and HRT is due to the treatment causing tumours to grow more rapidly and so be detected on tests. Whereas when fewer women use HRT, the tumours grow more slowly and so take longer to be detected and show up in official rates.

The findings were published online in Journal of the National Cancer Institute.

Dr Prithwish De, of the Canadian Cancer Society, and colleagues, found that use of HRT dropped from 12.7 per cent in 2002 to 4.9 per cent in 2004. During the same period breast cancer rates dropped by 9.6 per cent even though the same number of women were having mammography tests.

Between 2004 and 2006 use of HRT remained stable at around five per cent of women aged 50 to 59 but breast cancer rates began to increase again.

Dr De wrote: "The results support the hypothesised link between the use of hormone replacement therapy and invasive breast cancer incidence and indicate that the sharp decline in breast cancer incidence in 2002 is likely explained by the concurrent decline in the use of hormone replacement therapy among Canadian women.

"This hypothesis was supported by the temporal agreement of the trends in breast cancer incidence and use of hormone replacement therapy, especially given the absence of changes in mammography rates during the period of interest.

"In addition, the greatest decline in breast cancer incidence occurred among women 50–69 years, who are the predominant users of combined hormone replacement therapy."

The authors added: "Further evidence of a link between hormone replacement therapy and breast cancer is the rebound in cancer incidence rates observed in Canada since 2005. The largest hormone replacement therapy declines occurred among those older than 50 years, and the rebound in cancer incidence was also mainly restricted to women aged 50 years or older.

"Such a rebound might be expected if occult hormone-sensitive tumours were merely slowed by the withdrawal of hormone replacement therapy rather than prevented by it. If so, hormone replacement therapy may be thought to act as a promoter rather than as a putative cause of breast cancer. However, further follow-up data as well as information on the incidence trend of oestrogen receptor–positive breast cancer are needed to confirm this hypothesis and trend."

Dr Sarah Rawklings, Head of Policy & Education at the charity Breakthrough Breast Cancer said: "This study supports existing research into the link between HRT and breast cancer. It will be important to continue to study the effects of HRT on breast cancer incidence and development. Women who are concerned about this should contact their GP before starting, stopping or changing their HRT."