Combined HRT users 'twice as likely to develop breast cancer'

Women who use a certain type of hormone replacement therapy (HRT) are twice as likely to develop breast cancer as those who do not use any form of HRT at all, research showed today.

The study of more than one million participants found that post menopausal women using the combined oestrogen-progestagen treatment were at a greater risk than those using other types of HRT.

Research found the risk increased by 45% among users of tibolone, another form of the treatment, and by 30% among users of oestrogen-only HRT.

The UK study showed that if a woman stopped taking HRT, within a few years her risk of developing breast cancer dropped back to that of non-users.

In light of the study the British Committee on Safety of Medicines (CSM) has reviewed data and written to all health professionals.

Their advice, while not going as far as saying that women should stop taking HRT, says doctors should carefully discuss with their patients the risks and benefits of treatment and review each case individually.

They said the results of the study did not mean any urgent changes to women’s treatment were necessary.

Cancer Research UK’s Epidemiology Unit in Oxford monitored more than one million women between the ages of 50 and 64 who joined the study between 1996 and 2001.

Half the women were using HRT or had done so in the past. After 2.6 years of follow-up, 9,364 cases of breast cancer were found.

After 4.1 years, 637 breast cancer deaths were registered among all the women studied.

Past studies have shown a link between HRT and breast cancer risk, but this is the first and largest project to discuss the increased risks relating to different types of the treatment.

The study, published in The Lancet, said current users of HRT had a 22% increased risk of death from breast cancer, compared with women who had never used HRT.

However, the scientists noted this was of borderline statistical significance, and it was too soon to estimate the extra deaths linked to HRT.

Professor Valerie Beral, director of the epidemiology unit and lead author of the study, said the team estimated that in the past decade the use of HRT by women aged 50-64 in the UK had resulted in an extra 20,000 breast cancers.

She said that oestrogen-progestagen therapy accounted for 15,000 of these cases.

The combination treatment is usually given to women who still have a uterus, to avoid the increased risk of cancer in this area caused by oestrogen-only therapy.

“Since our results show a substantially greater increase in breast cancer with combined HRT, women need to weigh the increased risk of breast cancer caused by the addition of progestagen against the lowered risk of uterine cancer.

“Comparing the risks is by no means simple and women may well want to discuss options with their doctor.”

Professor Beral said there was “overwhelming evidence” that the risks of breast cancer were greater for combination HRT than other types.

She also noted that the risk increased significantly after one to two years of taking the drugs and increased further with duration.

Professor Beral highlighted the increased risk of combination treatment compared with oestrogen only by focusing on cases per 1,000 women.

Among 1,000 postmenopausal women who do not use HRT, there will be around 20 breast cancer cases between the ages of 50 and 60.

In every 1,000 women who begin 10 years of HRT at the age of 50, there will be five extra cases among oestrogen-only users and 19 among oestrogen-progestagen combination users.

This, Professor Beral noted, amounted to four times as many extra breast cancers among combination users than oestrogen-only users.

The CSM stressed that for most women, the benefits of having HRT would outweigh the risks.

“Each woman must be considered as an individual and we recommend that women’s cases are reappraised annually,” a spokeswoman said.

About one and a half million women in the UK are currently using HRT, with about half that number taking the combination treatment.

The Million Women Study, which along with Cancer Research UK was funded by the NHS Breast Screening programme and the Medical Research Council, was compiled using questionnaires from 1,084,110 women aged 50 to 64 who attended 66 breast-screening clinics.

This, Professor Beral said, amounted to a quarter of all women in this age group in the UK.

Details of the research can be found at www.millionwomenstudy.org.uk.