Friday 4 March 2005
In a study published this week, scientists at The Institute of Cancer Research have clarified the long-term risks of endometrial cancer (cancer of the womb) in breast cancer patients treated with the drug tamoxifen.
Most women are prescribed tamoxifen after surgery or chemotherapy for breast cancer. It is an effective drug which can prevent a recurrence of breast cancer, and studies have shown that it reduces the risk of cancer developing in the other breast. The benefits of taking tamoxifen still far outweigh the risks. It has been widely and successfully used, but in a small proportion of women can lead to the development of endometrial cancer.
This new study, the largest of its kind, has shown that women with breast cancer who are treated with tamoxifen are nearly 2½ times more likely than women not treated with the drug to go on to develop endometrial cancer, and that the risk increases with the length of time for which the patients are treated.
Professor Anthony Swerdlow, head of Epidemiology at The Institute of Cancer Research, comments:
“This study gives information to be considered when deciding on breast cancer treatment. Tamoxifen has brought great benefits in the treatment of breast cancer, but it is important to consider both the advantages and disadvantages of such treatment when prescribing it. We hope that our data will help to clarify this”.
The study examined 1880 patients, 813 of whom had been diagnosed with endometrial cancer after their breast cancer and 1067 of whom had had breast cancer, but not endometrial cancer. The risk of endometrial cancer increased in line with the duration of the tamoxifen treatment. The longer the woman had been taking the drug, the greater the risk. While the benefits of taking tamoxifen as part of early treatment for breast cancer outweigh the risks, current evidence does not suggest that treatment lasting longer than 5 years has any additional benefit.
Previous studies have established a link between tamoxifen treatment and endometrial cancer, but they have been smaller scale and focussed on recent and short-term use in postmenopausal women. Tamoxifen has different hormonal effects before and after the menopause. The scientists found that the effect of tamoxifen on risk of endometrial cancer, however, was similar in these two groups. Likewise, the daily dosage of the drug, which can vary from 10 mg to 40 mg per day, did not have any impact on risk. The crucial factor in determining the risk of endometrial cancer was the length of time for which tamoxifen had been taken.
Professor Peter Rigby, Chief Executive of The Institute of Cancer Research comments:
“We welcome the results of this study, which gives us much needed insight into risks for breast cancer patients taking tamoxifen over many years and provides valuable information for clinicians when determining long-term treatment and care”.
This work is supported by the Medical Research Council.
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For further information, or to arrange interviews, please contact:
Marie MacLean
Press Officer
Institute of Cancer Research
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Email: [email protected]
Notes to editors
- The benefits of taking tamoxifen still far outweigh the risks. There are also new drugs called aromatase inhibitors which are also used for breast cancer patients in similar circumstances.
- The Institute of Cancer Research is a centre of excellence with some of the world’s leading scientists working on cutting edge projects. It was founded in 1909 to carry out research into the causes of cancer and to develop new strategies for its prevention, diagnosis and treatment.
- The Institute is a charity that relies on voluntary income. The Institute is a highly cost-effective major cancer research organisation with over 90p in every £ directly supporting research.
Please note:
Unfortunately the press office are unable to answer queries from the general public. For general cancer information please refer to The Institute's cancer information page.