Women's Health: Breast cancer rates fall in wake of HRT study

Breast cancer rates are falling, and researchers think it's because fewer postmenopausal women are using hormone replacement therapy (HRT).

The use of HRT began dropping in 2002 when a study called the Women's Health Initiative reported that pills containing the female hormones estrogen and progestin were associated with increased risks of breast cancer and heart disease.

In the U.S., HRT prescriptions dropped by 20 million (38 per cent) between July and December 2002. And a study by researchers at the M.D. Anderson Cancer Center in Houston showed a 6.7 per cent decline in new breast cancer diagnoses in 2003 compared with 2002.

Updated data now show U.S. breast cancer incidence in 2004 maintained the same low level reported in 2003, the lowest seen in approximately two decades.

This demonstrates that the link between breast cancer and HRT "is a pretty compelling relationship," says Donald Berry, the lead researcher. "It doesn't prove cause, but the association is really quite remarkable and therefore, it's a 'smoking gun' if you like."

The decline in breast cancer incidence occurred primarily in women ages 50 to 59 years and was mainly seen in tumours whose growth is stimulated by estrogen. Cancers in this group dropped by nearly 15 per cent, while the incidence of estrogen-receptor-negative tumours remained essentially unchanged.

The breast cancer incidence data in Berry's analysis was based on information from the U.S. National Cancer Institute's Surveillance, Epidemiology and End Results program, which is collected from nine cancer registries reporting on nine per cent of the U.S. population.

Berry says the findings don't imply that all women should stop their use of HRT. The risk of developing breast cancer from the use of these hormones is relatively small, and for some women the benefits of HRT are well worth the risk.