Women's College Research Institute

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Tamoxifen may increase risk of diabetes in some women

Fall 2011

Dr. Lipscombe

 In a population-based study recently published in the peer-reviewed journal Cancer, Dr. Lorraine Lipscombe, scientist at Women's College Research Institute, endocrinologist in Women's College Hospital's department of medicine and assistant professor at the University of Toronto, reports surprising findings about a commonly used breast cancer medication.

Lipscombe's team found that in older breast cancer survivors, tamoxifen is associated with a significantly increased risk of diabetes, even after adjustment for other risk factors.

"Tamoxifen is an important treatment for estrogen-receptor breast cancer that has been shown to improve breast cancer survival," says Lipscombe. "We found that diabetes was 24 per cent higher in women who were using tamoxifen treatment, not with previous tamoxifen users."

"This suggests that although current tamoxifen therapy may increase the risk of diabetes in people who are susceptible, this risk does not continue after the medication is discontinued."

The researchers suspect that the underlying mechanisms may be related to tamoxifen's estrogen-inhibiting effect. Evidence suggests that estrogen plays a role in regulating blood glucose levels, and indeed postmenopausal women, whose estrogen levels are naturally lower, have a higher prevalence of diabetes, weight gain, insulin resistance, and metabolic syndrome. Furthermore, postmenopausal estrogen replacement therapy has been shown to reduce the incidence of diabetes.

Although Lipscombe's study shows that tamoxifen may increase the risk of diabetes in susceptible individuals, the publication highlights the need for further research to investigate this potential new side effect.

"Women taking tamoxifen should not discontinue, but should discuss with their doctor getting tested for diabetes, particularly if they have other risk factors such as a family history or obesity," says Lipscombe.

This study was conducted with the support of funding provided by Cancer Care Ontario and the Ontario Institute for Cancer Research (through funding provided by the Ministry of Health and Long-Term Care and the Ministry of Research & Innovation of the Government of Ontario) and by a Canadian Diabetes Association/CIHR-Institute of Nutrition, Metabolism and Diabetes Clinician Scientist Award, which also provides salary support for Dr. Lipscombe.

Read Cancer article

Lipscombe LL, Fischer HD, Yun L, Gruneir A, Austin P, Paszat L, Anderson GM, Rochon PA. Association between tamoxifen treatment and diabetes: A population-based study. Cancer. 2011 Sep 20 [Epub ahead of print].

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