A study published in The Lancet Oncology, shows women taking Hormone Replacement Therapy (HRT) are less likely to develop breast cancer. Researchers from the Fred Hutchinson Cancer Research Center, Seattle, USA looked at data from more than 7,500 women who were enrolled in the Women’s Health Initiative (WHI) trial and took HRT over a period of about six years.

The scientists found that those who took the HRT were around 20% less likely to develop breast cancer and significantly less likely to die from the disease than those who never used HRT. The protection appears to last years after the women stopped the HRT treatment.

Garnet Anderson, lead author of the study said:

“These latest results should provide reassurance about breast safety of oestrogen use for durations of about 5 years for women with a hysterectomy seeking relief from postmenopausal symptoms.”

Previous studies have been less conclusive with a 1993 initiative using equine estrogen for around 11,000 postmenopausal women aged 50 to 79, having to be stopped early, due to risk of blood clotting and stroke. The same problems have recently plagued the third generation birth control pills, with estrogen appearing to have the same risks for younger women.

Estrogen in birth control pills is also seen to increase breast cancer risk, so the new findings from Anderson and colleagues will be comforting to women who have to rely on HRT. They followed 7645 women (78% of the original surviving members) who were tracked from March 2005 until August 2009, a median (midpoint) 4.7 years after stopping estrogen therapy. The results in summary are quite clear:

  • 23% reduction in the incidence of invasive breast cancer against placebo.
  • 151 cases, 0.27% per year vs 199 cases, 0.35% per year on placebo.
  • Follow-up period of nearly 12 years, showed women in the oestrogen group who did develop breast cancer had a 63% reduction in deaths from the disease.
  • Six deaths, 0.009% per year vs 16 deaths, 0.024% per year on placebo.
  • The lower risk of breast cancer was restricted to women without a history of benign breast disease or a strong family history of breast cancer.

Researchers state that:

“The continued postintervention effect of oestrogen on breast cancer incidence is akin to that reported for other hormone-targeted drugs shown to reduce breast cancer incidence.”

The authors caution:

“Our data do not support the use of oestrogen for breast cancer risk reduction in light of the lack of benefit noted in populations at higher risk (including those with a strong family history of breast cancer or benign breast disease) and the additional risk of stroke and blood clots.”

In an accompanying Comment Anthony Howell from the University Hospital of South Manchester, UK, and Jack Cuzick from Queen Mary, University of London say:

“The WHI investigators should be congratulated for providing insight concerning the value of CEE and young women can be reassured of the low risks and potentially striking benefits, provided that they are counselled about the small increases in thromboembolic disease as noted with most hormonal preparations.”

Written by Rupert Shepherd