Drug that halves a woman’s risk of breast cancer works for SEVEN YEARS after they stop taking it

A drug that halves the risk of women getting breast cancer works seven years after they stop taking, scientists have found.

Anastrozole – branded as Arimidex – blocks oestrogen, which fuels most tumours. It only works in post-menopausal women. 

Previous research has shown the drug can halve the risk of breast cancer in women who take the drug for five years.

But now, a study of almost 4,000 women around the world found it offers protection for a further seven years after, totalling 12 years.

Anastrozole, a 4p-a-day pill, works the same as well-known wonder drug tamoxifen – but has been shown to have longer-lasting effects. 

It is already available on the NHS, but researchers at the Queen Mary University of London said the uptake by women at risk of breast cancer was low.   

Anastrozole, prescribed under the brand name Arimidex, halves a woman’s risk of breast cancer for seven years after she stops taking it, scientists have found

Lead author Professor Jack Cuzick said: ‘Previous research confirmed anastrozole is very effective while women are still taking the drug.

‘But this is the only trial looking at whether it offers long term protection for women at high risk of developing breast cancer.

‘After a detailed analysis… we have concluded it is highly effective in reducing breast cancer occurrence for at least 12 years.’

The study, published in medical journal The Lancet, involved 3,864 women whose health was recorded over the course of 12 years. They took anastrozole for five years.

Forty-nine per cent fewer breast cancers were diagnosed in the half who were given anastrozole – even in women who stopped taking it after the first five years. 

This is better than the 28 per cent decrease recorded for tamoxifen.

Dr Ivana Sestak, an expert in medical statistics at Queen Mary, said: ‘The findings mean that for every 29 women taking anastrozole for five years, one case of breast cancer will be prevented during a 12 year period.

‘Around 49 women would need to take tamoxifen for five years to prevent one breast cancer case during the same period.’


Arimidex, manufactured by AstraZeneca, is an oestrogen-blocking pill taken once a day.

Some breast cancers are stimulated to grow by the hormone oestrogen. These are known as oestrogen receptor positive or ER+ breast cancers.

It is used to treat postmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer after treatment to reduce the risk of the cancer coming back.

It is also for postmenopausal women diagnosed with advanced-stage or metastatic hormone-receptor-positive breast cancer.

Anastrozole may be given to reduce the risk of breast cancer in women who haven’t had breast cancer but have an increased risk of developing it because of their family history or risk factors. 

Because Arimidex lowers the amount of oestrogen in the body, it can cause side-effects of bone thinning and weakening and a higher-than-average risk of broken bones.  

There have been concerns around the side-effects of Arimidex, such as joint stiffness, bone thinning, hot flushes and vaginal dryness.

But 75 per cent of the women taking the drug were able to stick with it, compared with 77 per cent taking a placebo. 

This indicates even during treatment that side-effects were not severe enough to significantly deter women from taking the drug. 

The researchers said anastrozole or Arimidex, manufactured by AstraZeneca, should be the ‘drug-of-choice’ for post-menopausal women at increased risk of developing the disease. 

Professor Cuzick, who is co-chairman of International Breast Cancer Intervention Studies (IBIS), presented the findings at the San Antonio Breast Cancer Symposium in Texas.

He said: ‘This is an exciting finding which makes a strong case for anastrozole being the drug of choice for post-menopausal women at high risk of developing breast cancer.

‘Tamoxifen could be offered to the relatively few women who experience serious side-effects from anastrozole.’

Longer follow-up studies will be needed to evaluate whether anastrozole can reduce deaths from the disease.

The latest report also confirms that anastrozole does not have the same type of long term side-effects associated with tamoxifen – including endometrial cancer which begins in the lining of the womb.

However, only tamoxifen can be given to younger women. 

Aromatase inhibitors (AIs) like anastrozole are not given to premenopausal women because their ovaries still produce oestrogen. AIs will not stop the ovaries from making the oestrogen that feeds the tumour.

Professor Tony Howell, of the University of Manchester, who was involved in the study said: ‘Importantly, this study shows there are no significant long term side-effects in the five years after completion of anastrozole, particularly no increase in fractures or heart disease.’

The first phase of the study published in 2013, called IBIS-1, reported breast cancer occurrence among women taking the drug fell by 53 per cent during five years.

Post-menopausal women at high risk of developing breast cancer, due to family history and other risk factors, have been recommended to take the drug since 2017 in the UK and 2019 in the US. 

However, the drug is not currently offered to all the women who could benefit – possibly because some physicians are unsure of the evidence base for long term impact.

Professor Cuzick told the BBC: ‘Uptake has really been quite low. Currently it’s about 10 per cent of these women and we think it should be substantially higher.’

Experts believe tamoxifen could help prevent cancer in around 500,000 women in the UK but say the fear of side effects is putting them off. 

Just 15 per cent of high-risk women in a survey said they were taking the drug. Nearly three quarters were worried about possible side-effects.

Prof Charles Swanton, Cancer Research UK’s chief clinician, said: ‘Both tamoxifen and anastrozole can be given to women who are at higher risk of breast cancer.

‘Up until now we only knew tamoxifen has long lasting benefits, so it’s reassuring that this study looking specifically at anastrozole, which has fewer long term side-effects, gives better protection to women years after they stopped taking the drug.

‘Doctors may still decide that tamoxifen is more appropriate for some women, but it’s great there are options.

‘Anyone with questions about these findings, or about their family history and risk of breast cancer, should speak to their doctor, who can help work out which medication is best for them.’

Breast cancer is the most common cancer in women and affects over 55,000 UK women each year, killing more than 11,000.

It is estimated more than two million women across the world developed the disease last year – with more than 600,000 deaths.


Breast cancer is one of the most common cancers in the world. Each year in the UK there are more than 55,000 new cases, and the disease claims the lives of 11,500 women. In the US, it strikes 266,000 each year and kills 40,000. But what causes it and how can it be treated?

What is breast cancer?

Breast cancer develops from a cancerous cell which develops in the lining of a duct or lobule in one of the breasts.

When the breast cancer has spread into surrounding breast tissue it is called an ‘invasive’ breast cancer. Some people are diagnosed with ‘carcinoma in situ’, where no cancer cells have grown beyond the duct or lobule.

Most cases develop in women over the age of 50 but younger women are sometimes affected. Breast cancer can develop in men though this is rare.

Staging means how big the cancer is and whether it has spread. Stage 1 is the earliest stage and stage 4 means the cancer has spread to another part of the body.

The cancerous cells are graded from low, which means a slow growth, to high, which is fast growing. High grade cancers are more likely to come back after they have first been treated.

What causes breast cancer?

A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply ‘out of control’.

Although breast cancer can develop for no apparent reason, there are some risk factors that can increase the chance of developing breast cancer, such as genetics.

What are the symptoms of breast cancer?

The usual first symptom is a painless lump in the breast, although most breast lumps are not cancerous and are fluid filled cysts, which are benign. 

The first place that breast cancer usually spreads to is the lymph nodes in the armpit. If this occurs you will develop a swelling or lump in an armpit.

How is breast cancer diagnosed?

  • Initial assessment: A doctor examines the breasts and armpits. They may do tests such as a mammography, a special x-ray of the breast tissue which can indicate the possibility of tumours.
  • Biopsy: A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under the microscope to look for abnormal cells. The sample can confirm or rule out cancer.

If you are confirmed to have breast cancer, further tests may be needed to assess if it has spread. For example, blood tests, an ultrasound scan of the liver or a chest x-ray.

How is breast cancer treated?

Treatment options which may be considered include surgery, chemotherapy, radiotherapy and hormone treatment. Often a combination of two or more of these treatments are used.

  • Surgery: Breast-conserving surgery or the removal of the affected breast depending on the size of the tumour.
  • Radiotherapy: A treatment which uses high energy beams of radiation focussed on cancerous tissue. This kills cancer cells, or stops cancer cells from multiplying. It is mainly used in addition to surgery.
  • Chemotherapy: A treatment of cancer by using anti-cancer drugs which kill cancer cells, or stop them from multiplying
  • Hormone treatments: Some types of breast cancer are affected by the ‘female’ hormone oestrogen, which can stimulate the cancer cells to divide and multiply. Treatments which reduce the level of these hormones, or prevent them from working, are commonly used in people with breast cancer.

How successful is treatment?

The outlook is best in those who are diagnosed when the cancer is still small, and has not spread. Surgical removal of a tumour in an early stage may then give a good chance of cure.

The routine mammography offered to women between the ages of 50 and 70 mean more breast cancers are being diagnosed and treated at an early stage.

For more information visit breastcancercare.org.uk or www.cancerhelp.org.uk