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Tamoxifen may increase risk of diabetes in susceptible women

Oct. 17, 2011

Dr. Lorraine LipscombeIn a population-based study recently published in the peer-reviewed journal Cancer, Dr. Lorraine Lipscombe, scientist at Women’s College Research Institute and endocrinologist, reports surprising findings about a commonly used breast cancer medication. Her 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 post-menopausal women, whose estrogen levels are naturally lower, have a higher prevalence of diabetes, weight gain, insulin resistance and metabolic syndrome. Furthermore, post-menopausal 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. 


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