Four drug types have been found to reduce breast cancer incidence by 38% in women at an increased risk of the disease, according to a Cancer Research UK study published in The Lancet.
The study calculates that one breast cancer would be prevented for every 42 women who took the drug for five years and followed for a further five.
Researchers examined the records of more than 83,000 women to review the effectiveness of four specific but similar drugs - tamoxifen, raloxifene, arzoxifene, and lasofoxifene.
The drugs have the ability to lock on to the part of the breast cancer that the hormone oestrogen can attach to and stimulate the cell to multiply, therefore stopping growth.
The first five years of taking the drug showed the greatest fall in incidence, with 376 breast cancer cases versus 594 for those who were not taking these drug types; a fall of 4%.
There was also a 25% drop in breast cancer cases in the five years after the women had stopped taking the drug. But there was no effect on breast cancer deaths.
Professor Jack Cuzick, lead researcher based at the Queen Mary University of London, said: "These are very encouraging results and pave the way for more widespread use of these drugs in high risk women in a manner similar to the way statins and blood pressure lowering drugs are used to reduce the risk of heart disease and stroke."
Side effects included significantly increasing the risk of blood clots such as deep vein thrombosis and one of the four - tamoxifen - showed an increase in endometrial cancers. The increase in these cases fell after women stopped taking the drug.
The drugs also led to a reduction in the risk of fractures.
Hazel Nunn, head of health information at Cancer Research UK, said: "These results provide some of the clearest evidence to date of the ability of these drugs to prevent breast cancer.
"The study also offers clarity on the frequency of side effects that can be expected from these drugs. Breast cancer is the most common cancer in the UK, and research like this has the potential to reduce the number of women diagnosed with the disease in the future."
Women currently use tamoxifen for five years as part of breast cancer treatment but it is not approved as a preventive drug for the disease in the UK.
NICE issued draft guidance in January 2013 saying tamoxifen should be recommended for women at high risk of breast cancer. Final guidance is expected later this year.
Nunn said the charity looked forward to the final guidance from NICE and potentially more options for women to reduce risk of breast cancer.
But she added: "These drugs have a range of side-effects though, so they will not be suitable for all women. We urge them to discuss their options with their doctors."
