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Breast cancer rate falls with decline in HRT use

Incidence of breast cancer in Canada fell at the same time as HRT use

Louise Prime

Friday, 24 September 2010

As postmenopausal women’s use of hormone replacement therapy (HRT) has declined in Canada, so has the incidence of breast cancer in this population, shows a study published online in The Journal of the National Cancer Institute.

HRT prescriptions for hormone therapy fell steeply in several countries around the world after the Women’s Health Initiative (WHI) trial reported from the US in 2002 that the risks of combined oestrogen and progestogen therapy outweighed the benefits. The incidence of breast cancer also started to fall at the same time.

Researchers set out to find whether a decline in HRT prescribing was linked to a fall in breast cancer incidence in Canada, and examined various data sets on women aged 50-69 years. They analysed data on HRT prescriptions, breast cancer incidence by age, mammography rates, and self-reported use of HRT.

They found that: “The nearly 10% drop in invasive breast cancer rates coincided with the decline in use of hormone replacement therapy reported among Canadian women aged 50-69 years”. HRT use fell most steeply soon after publication of WHI, from 12.7% in 2002 to 4.9% in 2004; during that same period, the incidence of breast cancer fell by 9.6% while mammography rates remained stable at 72%.

The study authors say that the decline in breast cancer incidence “is likely explained by the concurrent decline in the use of hormone replacement therapy among Canadian women”. They argue that the drop in the use of hormone therapy might be partly explained by media reporting of results from both the WHI and the Million Women Study in the UK, of elevated breast cancer risk with combined HRT.

In Canada, cancer rates began to increase again in 2005 among women aged 50-69 years, which the authors say might be further evidence of a link between hormone therapy and breast cancer: “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 a cause, of breast cancer.”

The authors acknowledge that their study was subject to limitations such as that data on HRT use was self-reported and did not include frequency or duration of use. Nor did they have data on receptor status of breast tumours.

They conclude that: “Further long-term surveillance studies of trends between hormone replacement therapy and breast cancer incidence can help reconcile the potential population-level associations of these two factors.”


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