Long term oestrogen-only hormone replacement therapy increases breast cancer risk

May 10 2006

According to new research women who take oestrogen-only hormone replacement therapy for 20 years or longer to treat the symptoms of menopause, put themselves at greater risk of developing breast cancer.

In a study by Wendy Chen of Brigham and Women's Hospital and Dana Farber Cancer Institute, Boston, it was found that the risk of breast cancer from oestrogen therapy increased with long-term use by women who had a hysterectomy but did not become significant until after two decades of use.

The researchers are suggesting that women who need to take oestrogen for long periods in order to delay the symptoms and conditions associated with aging such as osteoporosis, should possibly look for alternatives.

These latest results come hot on the heels of a study of more than 10,000 women by Stamford University in the US, which appears to dismiss any connection in the short to medium term and found no evidence of any increased risk in women who used the therapy for up to seven years.

Oestrogen-only HRT is commonly prescribed for women who have had hysterectomies, as it increases the risk of womb cancer; a hysterectomy removes all or part of the uterus. The oestrogen therapy is produced from pregnant horse urine.

It was in 2002 that the results of the Women's Health Initiative study linked hormone therapy to an increased risk of ailments including stroke, blood clots and breast cancer.

Ever since a plethora of conflicting results have indicated a wide range of advantages and disadvantages associated with the therapy, depending on a variety of factors.

As a rule hormone therapy is now generally prescribed at the lowest possible dose for the shortest period of time, a strategy which is supported by some manufacturers.

Chen and her team examined data from the Nurses' Health Study, beginning with 11,500 female nurses in 1980 who had a hysterectomy, and ending with nearly 29,000 nurses.

Throughout the study period, 934 women developed invasive breast cancers. of these 226 had never used hormones, and 708 had used oestrogen therapy.

The longer a woman used oestrogen, the higher her risk of breast cancer appeared to be.

Those who had been taking oestrogen for fewer than 10 years did not appear to have a higher risk than those who had never taken hormones; but those who had been taking the hormone for more than 20 years had a significantly increased risk.

Women who have not had a hysterectomy seeking relief from menopausal symptoms like hot flashes can take a combination of oestrogen and progestin, which is designed to prevent uterine cancer.

But the combination therapy is also associated with a higher risk of breast cancer even when taken for a shorter duration.

Experts say women should be aware that not all the causes of breast cancer are known and it is likely that a combination of several factors interact and increase a woman's risk.

They say women should discuss treatment options with their doctor and also remember that the risk of breast cancer increases with age whether a woman takes HRT or not.

The study is published in the Archives of Internal Medicine, a journal published by the American Medical Association.