1. Goodwin, Peter M.

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AMSTERDAM, Netherlands-Insulin treatment for women with diabetes was found to be associated with increased mammographic density (MD)-while diabetic control by diet or drugs was found to have the opposite association-in a study reported at the 10th European Breast Cancer Conference from the Danish Diet, Cancer and Health study group (Abstract 158).

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"We found that women who don't take any treatment-and just regulate their diabetes with diet-and women who take oral medication-have lower breast density than women without diabetes," said lead study author, Zorana Jovanovic Andersen, PhD, an Associate Professor of Epidemiology at the University of Copenhagen, Department of Public Health Center for Epidemiology and Screening in Copenhagen, Denmark.


"But women who take insulin have significantly higher breast density than women without diabetes," she said.


Diabetes Impacts Breast Density

Since high MD is one of the strongest predictors of breast cancer risk, the prospective study examined whether diabetes and its treatments were associated with MD in a cohort of 5,644 Danish women above the age of 50 years who attended mammographic screening between 1993 and 2001.


The group had a mean age of 56 years, and 3,180 (56.3%) had breasts categorized as mixed or dense. There were 137 of the women who reported diagnoses of diabetes, and the study noted the type of treatment they used: diet, oral medicines, or insulin. Forty-four of the women with diabetes who used dietary management alone and 62 who took oral medicines were only two-thirds as likely to have high MD (after adjustment for factors like BMI and menopausal status). But the remaining 31 women whose diabetes was treated with insulin had double the risk of having high MD.


"This is the first time we have documented that diabetes treatment has a different impact on breast density," Andersen noted, adding the study did not investigate cause and effect, but that up to now no investigation of the effect of treatments for diabetes on breast cancer risks had been undertaken.


When she was asked if she was surprised by the finding she said she was not, because insulin is a growth promoting agent. "So in that sense-biologically-it makes sense that this could also increase breast tissue density," she said. And she noted the data were reassuring for other treatments for diabetes. "For oral medication, this is the very first result [showing] that this doesn't affect breast density in the same way," she said.


Breast Cancer Risk

While the data bring no clinical message for treating diabetes, Anderson said women having mammography need to be aware of the association. "This may affect their screening performance. In women who have higher breast density, it may be more difficult to detect cancer by screening, so it would be relevant to tell the radiologist at cancer screening as it will affect the ability to detect cancers. They may have a need for additional screening," she told Oncology Times.


"Our study looked solely at the effect of insulin on breast density. Now we would like to extend our research by following up these women for breast cancer and observing the effect of different diabetes treatments on breast cancer risk. If we find a relationship, we need to examine whether a high MD is responsible, or whether other factors are involved.


"In the meantime, we would urge all women, both with diabetes and without, to take measures to reduce their risk of developing breast cancer through simple lifestyle changes, such as avoiding obesity, reducing alcohol consumption, and exercising," she said.


Chair of the European Breast Cancer Conference, Fatima Cardoso MD, Director of the Breast Unit at Champalimaud Clinical Centre in Lisbon, Portugal, said that, despite much research into the role of the insulin pathway in breast cancer, the exact mechanisms were still unknown. "This study shows clearly that a link between diabetes treatment and breast density, an important risk factor for the disease, has been made. I hope that these findings will lead to further research into the effect of cheap, easily-available drugs such as metformin, not just on breast density, but on breast cancer risk overall," she said.


Peter M. Goodwin is a contributing writer.


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