The daily pill reduces the amount of oestrogen – a hormone sometimes used by cancers to help them grow – produced by the body.
Trials have shown it can halve the incidence of breast cancer in post-menopausal women who are at elevated risk, including those with a family history.
The drug has been used to treat breast cancer for years and prescribed to a small number of patients as a preventative measure off-label since 2017.
But from today it will be officially licensed by the Medicines and Healthcare products Regulatory Agency (MHRA) as a preventative treatment, opening the door for thousands more to benefit.
Two other drugs are available to reduce the risk of breast cancer – tamoxifen and raloxifene but anastrozole is now considered to be the most effective.
NHS England said 289,000 women aged 50 to 69 who are at moderate or high risk of breast cancer could be eligible – though not all are expected to take the drug. Estimates suggest that if one in four started the treatment this could prevent 2,000 breast cancer cases over their lifetimes and save the health service £15million.
The drug will mean women can “live without fear of breast cancer”, said NHS chief executive Amanda Pritchard.
She added: “It’s fantastic that this vital risk-reducing option could now help thousands of women and their families avoid the distress of a breast cancer diagnosis.
“Allowing more women to live healthier lives, free of breast cancer is truly remarkable.
“And we hope that licensing anastrozole for a new use today represents the first step to ensuring this risk-reducing option can be accessed by all who could benefit from it.”
Some 47,000 people are diagnosed with breast cancer each year in England with eight in 10 cases found in women aged 50 and over. The disease claims around 11,500 lives, making it the fourth most common cause of cancer death in the UK.
It is the first drug to have its licence extended thanks to the Medicines Repurposing Programme, launched in 2021, which looks for opportunities to use existing drugs in new ways.
The scheme is hosted by NHS England with the support of the MHRA, the Department of Health and Social Care plus others.
It builds on the success of repurposing medicines during the pandemic.
Women who choose to take the drug as a preventative will receive prescriptions for five years with the effects expected to be long-lasting. A trial involving more than 3,800 women found the medication led to a 49% reduction in breast cancer cases over 11 years.
But the pill can cause side effects –including hot flushes, feeling weak, pain/stiffness in the joints, arthritis, a rash, nausea, headache, osteoporosis and depression.
Baroness Morgan of Drefelin, chief executive at Breast Cancer Now, said: “The extension of anastrozole’s licence to cover it being used as a risk-reducing treatment is a major step forward that will enable more eligible women with a significant
family history of breast cancer, to reduce their chance of developing the disease.
“For the past decade, Breast Cancer Now has been campaigning with clinicians, researchers and patients for drugs that are found to be effective and safe in new uses to reach people who could benefit – and we were thrilled when NHS England set up the Medicines Repurposing Programme.
“Anastrozole was the first drug to be supported by the programme and this paves the way for improving access to risk-reducing drugs
“We look forward to continuing our work with NHS England to further improve access to these drugs for everyone eligible.”
Health minister Will Quince said: “I’m delighted that another effective drug to help to prevent this cruel disease has now been approved.
“We’ve already seen the positive effect anastrozole can have in treating the disease when it has been detected in post-menopausal women and now we can use it to stop it developing at all in some women.
“This is a great example of NHS England’s innovative Medicines Repurposing Programme supporting the development of new ways
for NHS patients to benefit from existing treatments.”
Dame June Raine, MHRA chief executive, added: “This innovative Programme is essential to support and advance research into medicines that might be repurposed, increase access to life-saving medicines and, ultimately, improve patients’ lives.
“The MHRA welcomes applications for repurposed medicines and encourages early dialogue from companies or developers considering this.”