Women considered at risk of breast cancer should be given therapy - such as tamoxifen - to prevent onset of the disease, an international group of cancer specialists has concluded.

Writing in the Lancet Oncology, the panel of experts estimate that 10% of women in the higher risk category could benefit from taking drugs as a preventative strategy, just as millions of people at risk from heart disease take statins.

Tamoxifen has been approved by the US Food and Drug Administration as a preventative therapy, on the back of clinical studies showing that it reduces oestrogen-receptor positive invasive breast cancer (but not oestrogen-receptor negative forms) by as much as 43%. 

On the downside, the drug is associated with some pretty nasty side effects, including a higher risk of womb cancer and blood clots, so to better balance the risk-benefit equation the experts recommend that only women who have a 4% or higher risk of developing breast cancer within 10 years are offered it for disease prevention.

Eli Lilly's Evista (raloxifene) has also been cleared for prevention in the US, but although it seems to be associated with less severe side effects, it appears to be less effective than tamoxifen, reducing the risk of invasive breast cancers by about 23%.

Looking forward, if less toxic drugs currently in clinical trials, such as the aromatase inhibitors Arimidex (anastrozole; AstraZeneca) and Aromasin (exemestane; Pfizer) also prove effective against the disease, half of all post-menopausal women could eventually be taking breast cancer prevention therapy, said chairman of the panel Professor Jack Cuzick.

Predicting benefit 

"There’s strong evidence to show that drugs such as tamoxifen are effective at preventing breast cancer in women with greater than average risk of the disease," Cuzick concluded, but also stressed the importance of finding "ways of predicting who will respond, so drugs like this can be targeted at those most likely to benefit and least likely to experience side effects".

One such marker could be Increased breast density, which is thought to be a leading risk factor for breast cancer. 

"Early trial results suggest that where tamoxifen is shown to decrease density the risk of cancer decreases, [and] if this is confirmed in long-term studies, breast density could become a powerful way to identify high-risk women who could benefit from preventive treatments,” he noted.

Commenting on the findings, Julia Manning, head of think-tank 2020health said: “With Tamoxifen it sounds like it is too early to judge but we must always question expanding ‘risk indicators’ and medicalising the well.”