Insulin linked to breast cancer

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The majority of breast cancers arise in postmenopausal women, and according to a new study, higher-than-normal levels of insulin in these women may increase the risk of breast cancer. Researchers at the Albert Einstein School of Medicine at Yeshiva University, New York City, found that women with the highest levels of insulin were 50 percent more likely to develop breast cancer than women who had the lowest insulin levels.

"Among these women, the influence of insulin on breast cancer risk was quite high," says lead author Marc Gunter, Ph.D., assistant professor of epidemiology and population health at Einstein. "Women with the highest insulin levels in their blood were more than two times more likely to develop breast cancer than women with the lowest insulin levels." Moreover, "when we controlled for insulin, the association between obesity and breast cancer became much weaker," Dr. Gunter says. "This means that a large component of that obesity-cancer relationship may be mediated by insulin levels."

Obese women have high levels of estrogen and other hormonal imbalances that may play a role in triggering breast cancer. Elevated levels of insulin may be a factor as it stimulates the growth of breast cells in tissue culture. This is the first study to identify insulin's role in breast cancer, while controlling for estrogen levels.

The findings have important implications for prevention, and possibly treatment, of postmenopausal breast cancer, says Howard Strickler, M.D., M.P.H, who was senior author of the paper and a professor of epidemiology & population health at Einstein. "Research now needs to focus on ways to reduce insulin's effects on cell growth and replication in the breast while preserving its positive metabolic effects."