Scientists at Manchester University NHS Foundation Trust (MFT) have developed a new highly sensitive hormone blood test to assess the efficacy of the preventative breast cancer drug, anastrozole.

Anastrozole is currently the recommended preventative therapy for women in the post-menopausal stage who are at high risk of developing breast cancer.

MFT published the findings of the research in the Lancet Oncology journal. The research demonstrated that up to 25% of these post-menopausal women will not benefit from taking the medication.

It also showed that clinicians will be able to provide these patients with a customised treatment plan if they conduct routine hormone testing.

This will prevent thousands of women from experiencing negative effects of the drug, the NHS trust said.

According to the study, anastrozole would have little to no effect on a woman’s risk of breast cancer if her oestradiol levels were low.

As a result, these women might have avoided the medication’s potential five-year adverse effects, which frequently include hot flushes, pains, and low mood.

MFT medical genetics and cancer epidemiology consultant D Gareth Evans said: “These results indicate the importance of incorporating serum oestrogen levels into risk models, so women can be reassured despite other risk factors if their levels are low, and likewise, higher levels may make more women eligible for anastrozole.”

In postmenopausal women, anastrozozole reduces oestrogen levels, which would otherwise promote the growth of breast cancer cells.

The once daily 1mg tablet of the hormone therapy medication known to be an aromatase inhibitor is administered over five years.

It can only be taken by women who have gone through menopause as the medication cannot reduce oestrogen in women whose ovaries are still functioning.

Anastrozole has been suggested as a preventive treatment by the National Institute for Health and Care Excellence (NICE) since 2017.

The Medicines and Healthcare Products Regulatory Agency (MHRA) granted the medication a licence for use on the NHS in November 2023.

It was based on results from an earlier study from the IBIS-II preventive trial, which was funded by MFT researchers. The trial revealed that anastrozole lowers the incidence of breast cancer in postmenopausal women who are at increased risk by 49%.