Tamoxifen protects against breast cancer in long-term

In collaboration with the Press Association

The breast cancer drug tamoxifen has been shown to protect against the disease for at least 20 years in women who take the drug for five years.

“The landmark IBIS trials show the value of chemoprevention for women at high risk of breast cancer" - Dr Julie Sharp, Cancer Research UK

The IBIS-I trial (International Breast Cancer Intervention Study), led by Queen Mary University of London and funded by Cancer Research UK, has revealed that, among those using the drug breast cancer, rates fell by around a third.

Professor Jack Cuzick, study leader and head of the Centre for Cancer Prevention at Queen Mary University of London, said: “A healthy diet and increased physical activity can help to prevent breast cancer, but for high risk women a more powerful intervention is needed. This is where tamoxifen, which is already recommended by NICE, [has] a role to play.”

“The landmark IBIS trials show the value of chemoprevention for women at high risk of breast cancer and highlight just how important these large and long-term studies are,” said Dr Julie Sharp, head of health information at Cancer Research UK.

The study, published in The Lancet Oncology, examined the long-term risks and benefits of taking tamoxifen to prevent breast cancer in women at high risk of the disease. Those classed as high risk were aged 35-70, primarily with a family history of breast cancer.

A total of 7,154 pre and post-menopausal women were randomised to receive either tamoxifen or a matching placebo for five years. The health of all participants was then monitored after the treatment, with an average follow-up time of 16 years and maximum of 22 years.

A total of 251 women from the tamoxifen group developed breast cancer, compared to 350 from the placebo group - representing a reduction of 29 per cent.

Furthermore, oestrogen receptor (ER) positive invasive cancer, which accounts for two thirds of all breast cancers, was reduced by as much as 35 per cent.

But the study also highlighted tamoxifen’s side effects. In the group taking tamoxifen endometrial cancers were almost four times more likely – 15 endometrial cancers were diagnosed in the tamoxifen group compared to 4 in the placebo group.

“This follow-up of IBIS-I confirms that tamoxifen has a long-lasting effect in reducing cases of breast cancer in women at high risk of the disease. All these drugs have side effects so it’s important that women at high risk of breast cancer talk through their choices with their doctor to work out the best option for them,” said Dr Sharp. 

Professor Jack Cuzick added, “We hope these results will stimulate more women, particularly younger women, to consider treatment options for breast cancer prevention if they have a family history of the disease or other major risk factors.”


  • Cuzick, J., et al. (2014). Tamoxifen for prevention of breast cancer: extended long-term follow-up of the IBIS-I breast cancer prevention trial The Lancet Oncology DOI: 10.1016/S1470-2045(14)71171-4