Taking aspirin every day could cut the risk of developing breast cancer by almost a third, according to a study published today.
Scientists say the popular painkiller, which is already credited with helping prevent heart attacks and strokes, could become an important weapon in the fight against the most common form of cancer among women in the UK.
Dr Richard Sullivan, head of clinical programmes at the charity Cancer Research UK, said: "This just goes to show that sometimes the oldest drugs still have new tricks up their sleeves.
"Aspirin is derived from willow bark and there is evidence it was being used by the ancient Egyptians to help calm inflammation. It really is turning into something of a wonder pill."
The study was published in the Journal of the American Medical Association. Researchers at Columbia University in New York carried out detailed interviews involving 1,400 breast cancer victims and 1,400 healthy women.
They looked at how many women were using the pills regularly to relieve problems such as headaches. They found that using aspirin at least once a week for six months led to a 20% lower risk of breast cancer. Using seven or more tablets in a week resulted in a 28% cut.
The effects were strongest in women with hormone receptor positive breast tumours, a form of the disease which affects 60% of sufferers.
The study also found that women using another form of painkiller, ibuprofen, also saw a reduction in risk but the effect was weaker than for aspirin. Their risk fell by 8% if they used ibuprofen three times a week or more.
There are 40,000 cases of breast cancer a year in Britain and 13,000 deaths. A woman's lifetime risk of developing the disease is about one in 12.
Aspirin is already taken daily by more than 2 million angina sufferers and heart attack survivors in the UK to protect against further attacks.
It is thought aspirin reduces the risk of cancer by interfering with the body's production of oestrogen. Past studies have suggested that the drug could reduce the risks of developing cancer of the pancreas, cancer of the ovaries and Hodgkin's disease although none of the studies have been able to say definitively whether it is aspirin which reduces the risks.
Last night experts agreed that more work was needed to assess the true potential of aspirin in the fight against the disease. Dr Sullivan, of Cancer Research UK, said: "We need a lot more work on this before doctors can make recommendations to women." But researchers who conducted the study said their findings added weight to the idea that aspirin could prove affective in the fight against breast cancer.
The report concluded: "These data add to the growing evidence that supports the regular use of aspirin and other non-steroidal anti-inflammatory drugs as effective chemopreventive agents for breast cancer."