UNLOCKING PERSONALISED PREVENTION: HOW HORMONE LEVELS GUIDE CANCER PREVENTION IN POSTMENOPAUSAL WOMEN

There is a groundbreaking approach to breast-cancer prevention in postmenopausal women – blood tests. Measuring hormone levels can identify women who would most benefit from anastrozole, a drug aimed at preventing breast cancer.

The IBIS-II clinical trial results were published in Lancet Oncology in December 2023 and shared at the San Antonio Breast Cancer Symposium.

The research delves into whether oestrogen levels in blood can pinpoint postmenopausal women at an elevated risk of developing breast cancer who would benefit from anastrozole’s preventive properties. The international randomised controlled IBIS-II prevention trial included nearly 4000 women globally, with 818 participants from Australia and New Zealand, and was spearheaded by Breast Cancer Trials in Australia and Cancer Research UK internationally.

Anastrozole belongs to a class of drugs known as aromatase inhibitors, recommended by the National Institute of Clinical Care and Excellence (NICE) for preventive therapy in high-risk postmenopausal women. These drugs halt oestrogen production, thereby reducing it in the body and they are the most potent preventive agents for oestrogen-receptor positive breast cancer. However, pinpointing those who would benefit most from these drugs would make them even more useful.

A nuanced analysis involved a case-control study of 212 women (72 cases, 140 controls), and revealed a marked trend: increased breast cancer risk correlated with rising hormone levels in the placebo group, a trend absent in the anastrozole-treated group. Notably, threequarters of women treated with anastrozole had a 55% reduction in cancer risk, with a diminished reduction noted among those with the lowest estradiol/sex hormone-binding globulin ratios.

“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,” said Dr. Nicholas Zdenkowski, the BCT Study Chair for the IBIS-II clinical trial. “This personalisation would allow for women to receive the medication that would offer them the best balance of managing cancer risk and side effects.”

Publication:
Cuzick, J., Chu, K., Keevil, B., Brentnall, A. R., Howell, A., Zdenkowski, N., Bonanni, B., Loibl, S., Holli, K., Evans, D. G., Cummings, S., Dowsett, M. (2023). Effect of baseline oestradiol serum concentration on the efficacy of anastrozole for preventing breast cancer in postmenopausal women at high risk: a case-control study of the IBIS-II prevention trial. Lancet Oncology. Published Online December 6, 2023. https://doi.org/10.1016/S1470-2045(23)00578-8