Hormone replacement therapy (HRT) has a huge role in increased breast cancer incidence, new research warns.

A new study at the University of Texas in the US has shown that falling breast cancer rates are linked to the lessening use of HRT, an extremely common treatment for menopausal women until a few years ago, and still widely used.

The researchers say that in the last few years there has been a decline in breast cancer for women aged 50-69, predominantly seen in oestrogen-receptor(ER)-positive cancer - the type of tumours fuelled by oestrogen, a hormone that is supplemented in HRT. Such cancers declined 14.7 percent in this time period, the same time period during which HRT became unfashionable after experts warned that the health risks outweighed the benefits.

"This kind of study can't prove causality, but the data present a very compelling link between hormone replacement therapy and breast cancer," says Dr Donald Berry, the study's senior investigator.

They found that the total decrease in breast cancer incidence was 6.7 per cent between 2002 and 2003. They also calculated that by the end of 2002, about 20 million fewer prescriptions for HRT were written in the United States- a decrease of 38 percent.

This means that stopping use of HRT may have prevented as many as 14,000 breast cancers in 2003 compared with 2002, in America alone.
A similar pattern has been noted in the UK after comparable findings were reported by Cancer Research UK in 2003.

The researchers suggest that women use the drug at the lowest dose and for the shortest time period to control hot flashes and other debilitating symptoms caused by the onset of menopause.

"The risk of developing breast cancer from use of these hormones is relatively small and for some women with postmenopausal symptoms, the benefits of HRT are well worth that risk," says Berry. "This is just another small piece of the puzzle to help women gauge the risks and benefits of using HRT."

This study may lead to new insights into both the etiology of breast cancer and its prevention.

There have also been several studies in favour of HRT. (Read more: The Menopause & Memory).

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