Hormone therapy increases the risk of breast cancer by a third, warns one study

Hormone replacement therapy (HRT) increases the risk of breast cancer by a third – twice as much as previous estimates.

And a major study shows that the danger persists more than ten years after the menopausal treatment.

This means that HRT is responsible for one in 20 breast cancers, say the researchers. This also makes it one of the major triggers of the disease after smoking, they warn.

Professor Richard Peto, a researcher at the University of Oxford, said: "I do not want to be alarming, but I do not want to be reassuring either.

"He will be responsible for more than 5% of all breast cancers."

In the United States, the average age of menopause is 51, with common symptoms including hot flashes, mood swings, loss of sexual desire, and vaginal dryness.

An estimated 12 million women use HRT in Western countries to fight the symptoms.

But this latest study shows that 8.3% of women who have the most common form for five years would be diagnosed with breast cancer over the next 20 years. The rate for those who had no treatment was one-third less than 6.3%.

Once a woman stopped using the treatment, the extra risk disappeared, but the study of 569,000 women showed that the risk had lasted a decade.

European and US regulators recommend the use of HRT as quickly as possible.

"These are real risks," said Professor Valerie Beral.

"We are really concerned that many generalists say it's something you do not have to worry about."

But Professor Martin Marshall of the Royal College of GPs said, "There is still plenty of evidence to suggest that HRT is safe and effective."

According to the organization of breast cancer, about 1 in 8 American women will develop invasive breast cancer during her lifetime.