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Research offers hope for long term breast cancer prevention

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by Cancer Research UK | News

20 February 2007

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New results of a worldwide breast cancer prevention study1 confirm that tamoxifen – a well established treatment for breast cancer – also reduces the risk of breast cancer in women at increased risk of the disease.

The research published in the Journal of the National Cancer Institute* today also shows the protective effect of the drug continues for several years after treatment has stopped, while the risk of side-effects returns to normal levels.

Initial IBIS-I results2 released in 2002 showed tamoxifen reduced hormone receptor positive breast cancer by about one third in pre and postmenopausal women at an increased risk of the disease. Today’s results confirm that these benefits continue for at least another five years after treatment has stopped.

The IBIS-I study, funded by Cancer Research UK, involved 7,154 pre and postmenopausal women in seven countries with an increased risk of breast cancer. Women on the study were given either 20 mg of tamoxifen or a placebo (dummy pill) every day for five years. After an average follow up of 96 months, 142 breast cancers were diagnosed in women in the tamoxifen group and 195 in the placebo group.

Lead researcher Professor Jack Cuzick, from the Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, said: “These latest IBIS-I results* confirm that tamoxifen continues to help prevent oestrogen receptor positive breast cancer in women at an increased risk of the disease for at least five years after treatment has stopped. Additionally we found that almost all of the excess side effects reported on tamoxifen do not continue after treatment stops.”

Researchers found that serious side effects like blood clots and endometrial cancer limit the use of tamoxifen in helping to prevent breast cancer. These new IBIS-I data demonstrate that these serious side effects stop after women stop taking tamoxifen.

Tony Howell, IBIS co-chair and Professor of Cancer Prevention at the South Manchester University Hospitals Trust, said: “Previous studies have already shown that tamoxifen lowers the risk of developing breast cancer during active preventive treatment but this is the first time that clear evidence is available on the benefits and side-effects of tamoxifen after treatment with the drug has stopped. These findings together with the effectiveness results suggest that over a longer follow-up time the risk of side-effects decreases while the benefit of prevention continues.”

Kate Law, director of clinical trials at Cancer Research UK, said: “These results are promising for women at increased risk of breast cancer. They are important in furthering our knowledge of the role of tamoxifen in the prevention of the disease and also raising the possibility of making it available on a wider scale. We are now investigating drugs that could be more effective at preventing breast cancer and have fewer side-effects. We hope to provide women with as many options as possible in protecting themselves against the disease.”

Professor Jack Cuzick added: “This is a major step towards the approach now used for preventing heart disease, where the major risk factors – such as high blood pressure and cholesterol – are identified and managed before disease occurs. We are continuing our search for a preventive option which is safer and more effective than tamoxifen in our current trial.”

The follow on study to IBIS-1 is IBIS-2 which is currently recruiting post-menopausal women to see whether the aromatase inhibitor anastrozole is more effective at preventing breast cancer in post-menopausal women at increased risk. IBIS-2 will also investigate whether anastrozole has fewer side effects than tamoxifen. Results from IBIS-2 are expected in 2010.


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