Hundreds of thousands of women will be prescribed a daily pill that can reduce their risk of getting breast cancer, in what campaigners have called a “game-changing” breakthrough in preventive care.

Women with a family history of cancer will be able to get the drugs tamoxifen and raloxifene on the NHS as a protection against breast cancer, under new guidelines from the National Institute of Health and Care Excellence (Nice).

Around 50,000 women and 400 men are diagnosed with breast cancer every year, making it the UK’s most widespread cancer. One in five cases is associated with a family history of breast cancer.

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Until now women considered to be of moderate or high risk have been offered annual screening to pick up tumours early, or have opted to undergo masectomy surgery.

Most women who have already been diagnosed with breast cancer already use the anti-oestrogen drug tamoxifen. Studies have shown that it and three other drugs can reduce the incidence of cancer by as much as 40 per cent in women with an increased risk of the disease.

Five-year courses of tamoxifen and raloxifene will now be available for prescription on the NHS before breast cancer has developed.

“Today’s new guidelines are a game changer in the way we prevent breast cancer,” said Dr Caitlin Palframan, assistant head of policy at Breakthrough Breast Cancer.

“Our strongest tool in the fight against breast cancer is prevention, and these new guidelines are a fantastic leap forward in the way we prevent breast cancer developing in those at highest risk.”

Earlier this year, a comprehensive study of 83,000 women found that five-year courses of four drugs – tamoxifen, raloxifene, arzoxifene and lasofoxifene – could prevent one breast cancer for every 42 women who took them. Tamoxifen is used to treat the most common type of breast cancer, that accounts for around 80 per cent of cases.

Professor Mark Baker, the director of the Centre for Clinical Practice at Nice, said that people are considered as having a family history of cancer if a number of their relatives have had certain cancers such as breast, ovarian or prostate.

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A person’s risk varies depending on the number of relatives who had cancer and the age at which they first developed it.

Nice believes that around 3 per cent of all women aged 35 or older in England and Wales – a total of nearly 500,000 – could be eligible to receive either tamoxifen or raloxifene pills for breast cancer prevention.

The cost to the NHS would be relatively low as the drugs are unbranded, generic medicines. Drugs trials have been going on for many years and tamoxifen has been prescribed in the USA since 2000, said Professor Tony Howell, scientific director of the Genesis breast cancer prevention charity.

“It’s a tremendous development that has been made on the basis of the efforts of all the women who were in our trials,” he said.

The decision to finally prescribe the drugs before diagnosis represented the biggest breakthrough in breast cancer prevention since the discovery of the breast cancer genes BRCA1 and BRCA2 in the mid-90s, he added.

Baroness Delyth Morgan, chief executive of Breast Cancer Campaign, said: “This is a truly historic moment in the treatment of women at increased risk of breast cancer, as we are witnessing a fundamental change of clinical practice driven by medical research.”

“It is worth remembering that chemo- prevention drugs have side effects and will not have the same risk-reducing impact for these women as preventive surgery – the choice recently made by Angelina Jolie – and the decision of what is right for each woman depends on the individual risk they face and their personal choice based on their own circumstance.”

The drugs have been linked to an increased risk of blood clots and one of tamoxifen’s side-effects includes a greater risk of cancers to the lining of the womb.

Tamoxifen, an anti-oestrogen drug is occasionally used to treat other cancers. Many cancers rely on the female hormone oestrogen to grow.

However, tamoxifen has been proven to be most effective against breast cancers, although the way it works is still not fully understood.

Tamoxifen

Tamoxifen’s main function is as an anti-oestrogen drug, but its function is still not wholly understood.

Many breast cancers rely on the female sex hormone oestrogen to grow. Tamoxifen blocks oestrogen from reaching the cancer cells. This means that the cancer either grows more slowly or stops growing altogether.

Raloxifene

Raloxifene works in a similar way. It will be used as an alternative to tamoxifen in older women who have already experienced the menopause.