IBIS-II Trial Results

Blood Hormone Levels Key to Identifying Postmenopausal Women Who Will Benefit Most from Anastrozole to Prevent Breast Cancer

An analysis of data from the IBIS-II clinical trial has found that hormone levels measured through blood tests, may be able to identify postmenopausal women who will benefit most from the breast cancer prevention drug anastrozole.

The study was published in the Lancet Oncology and presented at the San Antonio Breast Cancer Symposium in the United States.

Researchers tested whether measuring oestrogen in the blood could identify which postmenopausal women at increased risk of developing breast cancer, will benefit most from the preventive effects of an aromatase inhibitor. They analysed data from the IBIS-II prevention trial, an international randomised controlled trial of anastrozole in high-risk postmenopausal women.

The IBIS-II clinical trial enrolled almost 4,000 women worldwide, with 818 women from Australia and New Zealand across 30 institutions. The trial was coordinated in Australia by Breast Cancer Trials (BCT) and globally by Cancer Research UK.

Aromatase inhibitors such as anastrozole are recommended by the National Institute of Clinical Care and Excellence (NICE) as an option for preventive therapy in postmenopausal women at high risk of breast cancer.

Research has shown that postmenopausal women who have higher concentrations of the hormone oestrogen in their blood stream, are at higher risk of developing breast cancer. Aromatase inhibitors stop the production of oestrogen and reduce the amount made in the body. They are currently the most effective preventive agent for oestrogen-receptor positive breast cancer, but their utility could be increased by identifying those who stand to benefit most by taking these drugs.

In this new analysis of a case-control study of 212 women (72 cases, 140 controls), there was a clear trend of increasing breast cancer risk with increasing hormone levels in the placebo group, but not in the anastrozole group. A 55% reduction of risk of developing cancer was seen in three quarters of the women receiving anastrozole, but a lower reduction was seen in those with the lowest oestradiol/sex hormone binding globulin.

Dr Nicholas Zdenkowski is the BCT Study Chair of the IBIS II clinical trial and says the results of this research can help refine how we choose medications for patients at high risk of breast cancer.

“This data suggests that inexpensive blood tests to measure the ratio of these hormones, could be used to identify women who will benefit most from preventive therapy with an aromatase inhibitor,” Dr Zdenkowski said.

“In this analysis, 25% of these women with the lowest oestradiol measurements benefitted little from taking anastrozole, while still suffering from the side effects of the drug.

“This personalisation would allow for women to receive the medication that would offer them the best balance of managing cancer risk and side effects.”

Founded in 1978, Breast Cancer Trials conducts a multicentre national and international clinical trials research program, into the treatment and prevention of breast cancer. This involves over 900 researchers in 114 institutions across Australia and New Zealand.

For more information about Breast Cancer Trials, visit www.breastcancertrials.org.au