THE IBIS-I CLINICAL TRIAL

Preventing Breast Cancer for Women at High Risk

In what was a landmark breast cancer study, the IBIS-I clinical trial proved that tamoxifen reduces breast cancer rates for women with a high risk of developing the disease and that the benefit of the drug continues several years after treatment has stopped.

IBIS-I first started recruiting patients in 1992 and its aim was to look at whether the hormone therapy drug called tamoxifen could reduce the risk of breast cancer developing in women who are at high risk. Those classed as high risk were aged 35-70, primarily with the family history of breast cancer.

More than 7,100 patients worldwide participated in the IBIS-I clinical trial, including 2,674 from Australia and New Zealand. The trial was coordinated worldwide by Cancer Research UK and was conducted in Australia and New Zealand by Breast Cancer Trials.

Initial IBIS-I results released in 2002 demonstrated that tamoxifen reduced hormone receptor positive breast cancer by about one third in pre and post-menopausal women at increased risk of the disease.

Long-term follow up of IBIS-I released in 2006, found that tamoxifen reduces the risk of hormone receptor positive breast cancer by 34% in women at increased risk of the disease and that the benefit continues for at least several years even after treatment with the drug has stopped. This type of breast cancer accounts for two thirds of all breast cancers.

After completing treatment, the health of all trial participants was monitored with an average follow-up time of 16 years and a maximum of 22 years. In 2014, new extended analysis of tamoxifen showed that the preventative effect of the drug continues for 20 years.

Professor John Forbes AM was the Breast Cancer Trials Study Chair of the IBIS-I clinical trial.

“We know that tamoxifen is a well-established prevention drug for certain breast cancers. This analysis provides evidence of the long-term benefits of tamoxifen in women at high risk of the disease and IBIS-I has led to new recommendations for the care of women,” said Professor Forbes.