A drug that reduces a woman’s risk of breast cancer continues to work long after they stop taking it, say researchers.
Anastrozole blocks the production of the hormone oestrogen, which fuels the growth of many breast cancers.
It is already available on the NHS, but researchers at Queen Mary University of London said only a tenth of eligible women were receiving it.
Cancer Research UK said the findings were reassuring.
Anastrozole can be given only after the menopause because it cannot suppress oestrogen in younger women.
It is already used as a treatment once breast cancer has been discovered, but now trials are focusing on preventing cancers emerging in the first place.
Previous research, has shown anastrozole reduces the risk of breast cancer during the five years women took the drug.
But now, trials on 3,864 women show those taking it had 49% fewer breast cancers, even seven years after stopping treatment.
“Breast cancer is the commonest cancer in women and continuing to rise very rapidly,” Prof Jack Cuzick, the director of the Wolfson Institute of Preventive Medicine at Queen Mary University of London has said.
Drugs to prevent breast cancer mean having breasts removed is no longer the only preventive treatment.
“Up until now we only knew that tamoxifen has long-lasting benefits, so it’s reassuring that this study looking specifically at anastrozole, which has fewer long-term side-effects, gives better protection to women years after they stopped taking the drug.
Doctors may still decide that tamoxifen is more appropriate for some women, but it’s great that there are options,” Prof Charles Swanton, Cancer Research UK’s chief clinician has said.