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Preventing breast cancer – the next big step

The Cancer Research UK logo
by Cancer Research UK | News

30 September 2003

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Cancer Research UK scientists will embark on the next big step towards preventing breast cancer with the launch of a major new trial called IBIS II1.

The ten year study will test a new drug called anastrozole2 and involve 10,000 healthy women who are at an increased risk of the disease. Anastrozole has already been shown to be the most effective hormone treatment for breast cancer but this will be the first time the drug has been examined as a preventive measure.

Researchers believe that, in post-menopausal women, anastrozole could reduce the risk of breast cancer by more than 50 per cent. Around 30,000 postmenopausal women are diagnosed with the disease in the UK annually, so if successful this intervention could lead to several thousand fewer women developing breast cancer each year.

The trial follows the successful IBIS-I study which showed that tamoxifen reduces the incidence of breast cancer by a third in women at a higher risk of the disease.

During trials of anastrozole as a treatment for early breast cancer3, researchers noticed that women taking the drug were around 40 per cent less likely to be diagnosed with a second cancer in the opposite breast compared to women taking tamoxifen.

Over 40 centres are now open for recruitment worldwide, including 20 in the UK4. The international research team will be led by Professor Jack Cuzick, Director of Cancer Research UK’s Department of Mathematics, Statistics and Epidemiology based at Queen Mary, University of London.

He explains: “The results of the earlier IBIS-I trial showed that preventing breast cancer is a real possibility, but the new trial has the potential to have an even more dramatic impact on the disease.”

Both anastrozole and tamoxifen work by interfering with the female hormone oestrogen, which is known to be the most important cause of breast cancer.

Tamoxifen works by preventing the action of oestrogen on the cells of the breast while maintaining the beneficial effects of oestrogen on bone. However, tamoxifen also produces oestrogen-like effects on the cells of the endometrium (womb lining) and is linked to a slightly higher rate of endometrial cancer and a tendency to thrombosis (blood clots).

Unlike tamoxifen, anastrozole actually prevents the production of oestrogen in post-menopausal women and seems to have fewer side effects.

Compared to tamoxifen, women taking anastrozole experience fewer hot flushes. However, anastrozole does not have the beneficial effects of tamoxifen on bones and this will be carefully monitored and managed within the trial.

Professor Cuzick adds: “It’s vital that in trying to prevent breast cancer we balance the beneficial effects of a drug with any potential side effects.

“All drugs have side effects but anastrozole has fewer than tamoxifen and in particular it doesn’t show the slightly increased risk of blood clots or womb cancer.”

To be eligible for IBIS II, women must be post-menopausal, not taking HRT and have at least twice the normal risk of breast cancer – for example someone whose mother or sister had breast cancer before the age of 50, or who has two family members with the disease.

The trial will compare anastrozole with a placebo and look at how many women develop breast cancer as well as any side effects of the drug.

It will be the first opportunity for women to take anastrozole as a preventive measure. Although only half of the women on the trial will receive the new drug, all of the women will receive a bone scan, breast screening every 18 months and the best available care and monitoring.

Among the 10,000 recruited, 4,000 will be women who have been diagnosed with a non-invasive form of breast cancer, called DCIS5. As well as being at an increased risk of developing fully invasive breast cancer, these women are also more likely to develop a new tumour in the opposite breast.

This section of the trial is designed to find out whether anastrozole can prevent the occurrence of new cancers, both in the breast affected by DCIS and the opposite one.

Kate Law, Cancer Research UK’s Head of Clinical Trials, says: “Today’s launch marks an important day for breast cancer research. With the incidence of breast cancer rising year on year it’s vital that we consider ways to prevent the disease.

“Anastrozole looks like a very promising option but the only way we will know for sure is to carry out this large scale trial. If the drug lives up to its promise thousands of cancers could be prevented in the UK alone.”



  1. International Breast cancer Intervention Study II
  2. Anastrozole’s trade name is Arimidex. It is one of a group of drugs called aromatase inhibitors. In post-menopausal women, an enzyme called aromatase is the main source of oestrogen. Aromatase inhibitors block the action of aromatase, reducing the levels of oestrogen in the body.
  3. The ATAC study – Arimidex and Tamoxifen Alone or in Combination.
  4. UK centres open to recruitment are: Northwick Park & St Marks Hospitals, Harrow; Bristol Haematology and Oncology Centre; Yeovil Hospital; Frenchay Breast Care Centre, Bristol; Leeds General Infirmary; Castle Hill Hospital, Cottingham; Derby City General Hospital; Queen Elizabeth hospital, Birmingham; Withington Hospital, Manchester; Guy’s NHS Trust, London; Royal Liverpool University Hospital; St. James’s Hospital, Leeds; University of Wales College of Medicine, Cardiff; Western General Hospital, Edinburgh; St Margaret’s Hospital, Epping; Royal Cornwall Hospital, Treliske; City Hospital, Nottingham; Chelmsford & Essex Centre; Royal South Hants Hospital, Southampton; South and East Dorset Primary Care Trust, Ferndown.
  5. Ductal carcinoma in situ (DCIS) is a form of breast cancer in the milkducts. As these cells are contained within the ducts, there is very little chance that any of the cells have spread to the lymph nodes or elsewhere in the body. Some doctors describe DCIS as a very early form of breast cancer, others call it a pre-cancerous condition because it often develops into an invasive cancer if it is not treated. These cases are usually only detected by mammographic screening, where they represent about 20% of the detected abnormalities (approximately 2,700 women each year).

For more information on the trial log on to the IBIS website or CancerHelp UK