How Insulin Levels Are Managed Affects Breast Density in Women With Diabetes

Diabetes treatments, such as diet or pills (eg, metformin), decrease mammographic density, whereas insulin may increase mammographic density, according to research presented at the 10th European Breast Cancer Conference.1

Past studies linked diabetes to mammographic density, but this is the first data connecting diabetes treatments and insulin use to mammographic density. Breast density, which is measured as mammographic density, is a strong risk factor for breast cancer. Risk for breast cancer is 4 to 6 times greater for women with high density breasts (more than 75% density) compared with women whose mammographic density is less than 25%.

This study's cohort included 5644 women—including 4500 postmenopausal women—who were recruited into the Danish Diet, Cancer and Health (DCH) study group, and who underwent mammographic screening between 1993 and 2001. Mean age was 56 years, and 137 (2.4%) participants had diabetes. More than half of the cohort (3180 women [56.3%]) had breasts that were categorized as mixed or dense.

"Women with diabetes were less likely to have mixed or dense breasts, as opposed to fatty ones, both before and after adjustment for other factors such as being overweight," said Zorana Jovanovic Andersen, PhD, associate professor of Epidemiology at the University of Southern Denmark, Esjberg, Denmark, and poster presenter.

Among the 44 women who controlled their diabetes with diet alone and the 62 women who took oral medication for their diabetes, their breast density was less likely to be categorized as mixed or dense. However, women with diabetes who took insulin via injections had higher odds of having their breast density categorized as mixed or dense. These associations were not modified by menopausal status or by body mass index (BMI).

"Diabetes is associated with an increased risk of breast cancer, but the exact mechanisms which bring this about are still unclear,” said Andersen.

“One of the characteristics of cancer cells is their ability to grow rapidly and uncontrollably, and to resist the programmed death that occurs in noncancer cells. Therefore, growth factors are critical to cancer development and progression. We know that insulin is an important growth factor for all body tissues, and even if we do not know exactly how it affects the development of cancer cells, it is also highly plausible that it increases breast density."

The researchers emphasized that their finding of an association between insulin treatment and increased mammographic density does not imply that the woman's breast cancer risk is increased.

"Breast density is only one of many risk factors for developing breast cancer," said Andersen.


1. Andersen Z, Buschard K, Thomassen K, et al. Diabetes, diabetes treatment and mammographic density in Danish diet, cancer, and health cohort. Poster presented at: 10th European Breast Cancer Conference; March 9-11, 2016; Amsterdam, The Netherlands. Abstract 158.

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