Women with a high risk of breast cancer could be prescribed drugs to prevent the disease.
New guidelines from the National Institute for Health and Clinical Excellence (Nice) recommend that post-menopausal women with a strong family history of breast cancer are given the option of taking medication to reduce their risk.
The move was hailed as "historic" by a leading breast cancer charity.
Between 3% and 5% of the 48,000 breast cancers each year are caused by genes that are passed down families. They raise the risk of the disease to around 80% - compared to 12% for the average woman.
Currently, women with one of the genes have regular mammograms to spot tumours early.
Some, including Sharon Osbourne, choose to have their breasts removed even though they are perfectly healthy, to reduce their risk to low levels.
But recent studies have shown that taking the drugs tamoxifen or raloxifene for five years can halve the risk of cancer. Nice says the evidence is strong enough to recommend so-called "chemoprevention".
The US Food and Drug Administration has already approved the drugs for preventing cancer.
Chris Askew, chief executive of Breakthrough Breast Cancer , said: "This draft guideline represents a 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."
Neither of the drugs is currently licensed for preventing cancer and Nice has warned that any doctor prescribing them would have to take "full responsibility for the decision".
The recommendation is part of new draft guidelines on familial breast cancer.
They also extend genetic testing to more women with relatives affected by the disease, as well as recommend regular MRI scans for younger women who carry high risk genes.
Professor Mark Baker, director of the Centre for Clinical Practice at Nice, said: "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."