Oestrogen-only HRT increases breast cancer risk, study finds

LONG-TERM oestrogen-only hormone replacement therapy for women who have had their wombs removed can increase the risk of breast cancer, researchers said today.

Oestrogen-only HRT is reserved for women who have undergone hysterectomies because of its association with womb cancer.

Other types of HRT, given to women with wombs, contain a combination of oestrogen and the synthetic hormone progestin.

Previous research has found a higher than normal rates of breast cancer in women taking the combination therapy over a long period.

The new investigation involved almost 29,000 women taking part in the Nurses Health Study in the United States between 1976 and 2002.

Women were asked every two years if they used hormones and whether they had developed breast cancer.

Throughout the study period, 934 invasive breast cancers developed, 226 among women who had never used HRT and 708 who had taken oestrogen.

The longer a woman had been using oestrogen, the higher was her risk of breast cancer.

Those who had been taking oestrogen for more than 20 years had a significantly increased risk, the researchers reported in the Archives of Internal Medicine.

The authors, led by Dr Wendy Chen, from Brigham and Women’s Hospital and Dana Farber Cancer Institute in Boston, Massachusetts, wrote: “In conclusion, we found that oestrogen therapy was associated with an increased risk of breast cancer with longer-term use.

“Women who take oestrogen therapy for prevention or treatment of osteoporosis typically require longer term treatment, and should thus explore other options, given the increased risk of breast cancer with longer term use.”

Taking oestrogen HRT for less than 10 years did not present a significant breast cancer hazard.

But another major US study, the Women’s Health Initiative, has previously shown an increased risk of stroke and deep-vein thrombosis in women on oestrogen therapy for this time period.

Liz Carroll, Head of Clinical Services at the charity Breast Cancer Care, said: “This study confirms earlier work which concluded that taking oestrogen-only HRT for seven years or under does not increase the risk of breast cancer, but does suggest taking this type of HRT on a long-term basis (more than 10 years) significantly increases a woman’s risk.

“Women who are taking HRT for longer than 10 years should be aware of the potential risks and discuss possible alternatives with their doctor. However, all women should be breast aware, by knowing how their breasts normally look and feel and reporting any changes immediately. The risk of breast cancer increases with age whether you take HRT or not.”