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Repurposed drug halves breast cancer risk

Woman self-checking breast in mirror

Published: 16 November 2023

Tens of thousands of women in England could benefit from a drug that prevents breast cancer.

Anastrozole, a hormone blocker used for many years to treat breast cancer, has been licensed for preventative use.

It’s the first drug to be repurposed under the Medicines Repurposing Programme. This new multi-agency programme is supported by the NIHR

The drug will be offered to high-risk postmenopausal women. This includes those with a significant family history of the disease. It’s estimated that 300,000 women could be eligible for the preventative treatment. 

Drug halves risk of breast cancer

In 2013, the IBIS-II Prevention study found that anastrozole cut the risk of breast cancer in half in postmenopausal women.

Results were based on data from nearly 4,000 women, aged 40-70, in 18 different countries. Treatment involved taking 1mg tablets of anastrozole daily for 5 years or a placebo.

Many breast cancers rely on oestrogen to grow. After menopause, an enzyme in the body still makes small amounts of oestrogen by changing hormones called androgens into oestrogen. Anastrozole prevents this from happening by blocking the enzyme, called aromatase.

A follow up study, published in 2020, showed that the benefits of the drug extended beyond the 5-year treatment period

The international study was funded by industry, government and charity partners. It was supported by the NIHR Clinical Research Network (CRN), which recruited almost 1,500 volunteers across 48 sites in the UK

Dr Pippa Corrie, NIHR CRN National Specialty Lead for Late Phase and International Trials and chair of the CRN Cancer Specialty Group, said: "The IBIS-II trial was foundational to the decision to licence anastrozole for preventative use, and the NIHR CRN played a vital role in delivering this large-scale, international study - recruiting nearly 40% of the women who took part.

"It's exciting to see that our work, and that of our partners, continues to influence the delivery of care in England. The extension of anastrozole for preventative use could save thousands of women and their families the heartache of a breast cancer diagnosis."

NIHR early phase infrastructure, including Manchester Biomedical Research Centre (BRC) and the BRC at The Royal Marsden and the Institute of Cancer Research, has also been essential in the development and evaluation of anastrozole.

World-leading drug programme

Anastrozole was first recommended for preventative use by the National Institute for Health and Care Excellence (NICE) in 2017. But without a proper licence, uptake has remained low.

Last week it was licensed for prevention by the Medicines and Healthcare products Regulatory Agency (MHRA), as part of NHS England's medicines repurposing programme.

The pioneering programme builds on the successes of the COVID-19 pandemic - when tocilizumab, an arthritis drug, and dexamethasone, a widely available steroid, were both repurposed as treatments for COVID-19.

The Medicines Repurposing programme is supported by the Department of Health and Social Care, MHRA, NICE and NIHR.

Saving lives and NHS resource

Breast cancer is the most common type of cancer in the UK. Every year, around 56,000 women in the UK are diagnosed with breast cancer – about 150 a day. While survival rates have improved, 11,500 people still die from it each year.

Not all will choose to take anastrozole. But if 25% of eligible women do, it could prevent 2,000 cases of cancer. This would save the NHS around £15 million in treatment costs. 

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