Finding the best candidates for a breast cancer prevention drug

Oestrogen levels measured through blood tests may be able to identify postmenopausal women who will benefit most from the breast cancer prevention drug anastrozole, according to international research published in The Lancet Oncology.

Research has shown that postmenopausal women who have higher concentrations of oestrogen in their bloodstream are at higher risk of developing breast cancer. Aromatase inhibitors such as anastrozole stop the production of oestrogen and reduce the amount made in the body, and are recommended by the UK’s National Institute of Clinical Care and Excellence (NICE) as an option for preventive therapy in postmenopausal women at high risk of breast cancer. 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.

Researchers analysed data from the IBIS-II prevention trial, an international randomised controlled trial of anastrozole in high-risk postmenopausal women that was coordinated in Australia by Breast Cancer Trials (BCT) and globally by Cancer Research UK. In their 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, the BCT Study Chair of the IBIS-II clinical trial, said the results of the new 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,” Zdenkowski said.

“In this analysis, 25% of these women with the lowest oestradiol measurements benefited 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.”

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