Women with a family history of breast cancer who are thought to be at greater risk of developing the disease could be offered drugs aimed at preventing it under draft guidelines published Tuesday.
The National Institute of Health and Clinical Excellence (NICE) has launched a consultation on proposals to recommend the drugs tamoxifen or raloxifene for "high-risk" post-menopausal women.
Under the draft guidelines for England, Wales and Northern Ireland, women would be offered the hormone therapy drug for a five-year period in what the charity Breakthrough Breast Cancer called an "historic step".
Around 50,000 women in Britain are diagnosed with breast cancer each year and about one in five of those has a family history of the disease. Around 12,000 people a year die of breast cancer in Britain.
A clinical trial found that taking tamoxifen for five years halves the risk of developing invasive breast cancer for post-menopausal women with a high risk of getting the disease.
A separate trial found that taking raloxifene for five years reduces the risk of breast cancer for such women by about 38 percent.
If approved, the guidance on familial breast cancer, which was last updated in 2006, would also lower the age at which this category of women are offered breast screening.
Professor Mark Baker, director of the Centre for Clinical Practice at NICE, said: "The causes of cancer are complex and not fully known.
"However, we do know that having a family history of breast, ovarian or a related cancer can significantly increase the risk of developing breast cancer - including developing the cancer at a younger age.
"It is also more likely that people with family members affected by cancer who then develop breast cancer themselves could develop a separate tumour in the other breast following initial treatment.
"This is why it's wise for any person with a family history of cancer to receive appropriate investigations and screening that would otherwise be unnecessary if a family history did not exist."
Chris Askew, chief executive of Breakthrough Breast Cancer, said: "This draft guideline represents an historic step for the prevention of breast cancer - it is the first time drugs have ever been recommended for reducing breast cancer risk in the UK.
"This is exciting as, even though most women do not have a significant family history of the disease, it's crucial that those who do have an array of options to help them control their risk."