Women in England and Wales with a strong family history of breast cancer could be offered medication on the NHS to try to prevent the disease.
The National Institute of Health and Clinical Excellence has launched a consultation on whether tamoxifen could be given for up to five years.
If approved later this year, the draft guidelines would be the first of their kind in the UK.
Charity Breakthrough Breast Cancer welcomed the "exciting, historic step".
NICE says not enough is being done to help healthy but high-risk women, who include women with a sister and a mother or aunt diagnosed with breast cancer before the age of 50.
Taking tamoxifen for five years could cut their own risk of the disease.
Breast cancer is the most common cancer in the UK, with about 50,000 women and 400 men diagnosed with the condition each year.
Most cases occur by chance and with increasing age.
But having a family history of breast or ovarian cancer can significantly increase the risk of developing breast cancer and at a younger age, although most women with a relative with breast cancer are not at a substantially increased risk themselves.
NICE says under 1% of women fall into the high-risk category.
The new draft guidelines for England and Wales, which would update recommendations made by NICE in 2006, apply to these women and focus on areas of care where new evidence has been published, which includes using tamoxifen as a preventative treatment.
Based on research findings, experts estimate that for every 1,000 women given tamoxifen, there would be 20 fewer breast cancers.
But this would have to be balanced against the risks associated with taking the drug, such as blood clots.
Currently, both tamoxifen and raloxifene, a similar breast cancer drug, are not licensed for this indication.
Final NICE guidance is expected this summer.
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 the charity 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."
She urged women with concerns about their family history of breast cancer to speak to their doctor.