A common osteoporosis drug can shield women against the loss of bone mineral density – a side effect of the drug anastrozole which is taken to prevent breast cancer in the IBIS-2 study – according to new data presented at the San Antonio Breast Cancer Symposium.

The data being presented are from the IBIS-2 Bone Sub Study. IBIS-2 is a breast cancer prevention trial looking to see if the drug anastrozole can prevent breast cancer in women at high risk of the disease. The bone sub study has been designed to examine the effects of anastrozole on bone mineral density and whether the extra risk of developing osteoporosis or fractures among women taking part in IBIS-2 can be reduced or even eliminated.

Early results showed that after one year on the trial those women taking a type of osteoporosis drug called bisphosphonate had increased bone mineral density. This increase is despite the women starting the trial with low bone mineral density and being at higher risk of osteoporosis.

Anastrozole is currently only used as a treatment for breast cancer and the only women in the UK using the drug for prevention are those taking part in the IBIS-2 trial. Anastrozole works by blocking the production of oestrogen. By reducing the levels of oestrogen in the body the researchers are hoping to stop those breast cancers that rely on oestrogen from growing. It is also this reduced level of oestrogen that can reduce bone mineral density.

Dr Shalini Singh, who leads the bone sub study and presented the data, said: “Research into the effect that anastrozole has on women’s bones and the extent to which a bisphosphonate can help counter this continues. These preliminary, one year data are encouraging though and we look forward to the three year results to see if this effect is maintained.”

Professor Jack Cuzick, IBIS-2 co-chairman, who is based at Cancer Research UK’s centre for Epidemiology, Mathematics and Statistics, said: “Although these are still very early results, they are reassuring for women participating in the IBIS-2 trial and also for those who may be taking anastrozole as part of their treatment for breast cancer. We still need more eligible women to come forward and take part in this study, which aims to provide them and future generations with valuable information on how to help prevent and control breast cancer.”

For more information on the trial, please visit the IBIS website, CancerHelp UK or call the Cancer Research UK cancer information nurses on 0808 800 4040.


For media enquiries please contact the Cancer Research UK press office on 020 7061 8300 or, out of hours, the duty press officer on 07050 264059.


IBIS-2 (International Breast cancer Intervention Study II) is a ten year study involving 10,000 healthy women who are at an increased risk of breast cancer.

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IBIS-2 is being coordinated by Cancer Research UK and sponsored by Queen Mary, University of London. The trial is taking place in 21 countries, including Australia, India, Chile, Germany and Italy.

The IBIS-2 Prevention part of the study aims to recruit 6,000 post-menopausal women who are at increased risk of developing breast cancer. A number of factors for increased risk can make a woman eligible to enter the study and these are set according to the different age groups. Women can take part in the trial if they are aged between 40-70 years and are not on HRT.

IBIS-2 DCIS will recruit 4,000 postmenopausal women who have been diagnosed with and had surgery to remove DCIS (Ductal carcinoma in situ). This part of the trial is designed to determine which of the two drugs, anastrozole or tamoxifen, can best prevent new cancers, both in the breast affected by DCIS and in the opposite breast. Women who have had a mastectomy to remove their DCIS cannot join this arm of the trial but they can be part of the prevention part.