Metabolic Factors May Play a Role in Risk for Breast Cancer

Physiological changes associated with the metabolic syndrome may play a role in the risk of postmenopausal breast cancer, according to study results published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

The metabolic syndrome, or insulin resistance syndrome, consists of a constellation of factors including abdominal obesity, high blood glucose levels, impaired glucose tolerance, abnormal lipid levels and high blood pressure.

Affecting roughly 47 million Americans, the metabolic syndrome is also associated with poor diet and lack of physical activity. It can also increase the risk for diabetes and heart disease.

The metabolic syndrome is characterized by elevated insulin levels, and in recent years scientists have proposed that insulin may contribute directly or indirectly to the development of breast cancer. Researchers suspect that the metabolic syndrome could influence the risk for breast cancer by affecting interrelated hormones, such as insulin, estrogen, cytokines and growth factors.

“This study suggests that having the metabolic syndrome itself or some of its components may increase a woman’s risk of postmenopausal breast cancer. However, much more work is needed to understand the role of these metabolic factors and their interplay with better established breast cancer risk factors, such as reproductive and hormonal factors,” said researcher Geoffrey C. Kabat, Ph.D., senior epidemiologist in the department of epidemiology and population health at Albert Einstein College of Medicine, New York.

Studies to date have evaluated individual components of the metabolic syndrome and breast cancer, with inconsistent results, according to Kabat. For the first time, Kabat and colleagues assessed whether women who met the criteria of having the metabolic syndrome were at greater risk for postmenopausal breast cancer.

In this longitudinal study, the researchers used existing data from the Women’s Health Initiative — a large, national study designed to assess major causes of chronic disease in women. Participants included postmenopausal women aged 50 to 79 years at enrollment who had repeated measurements of components of metabolic syndrome over an eight-year period. These included blood levels of glucose, HDL-cholesterol and triglycerides, as well as waist girth and blood pressure.

Results showed a modest positive association of having the metabolic syndrome as a whole, according to Kabat. Of the 4,888 women with baseline measurements who did not have diabetes, 165 incident cases of breast cancer were diagnosed during the follow-up period. Presence of the metabolic syndrome at baseline was not associated with breast cancer risk.

However, in analyses that made use of the repeated measurements, “women who had the metabolic syndrome during the three to five years prior to breast cancer diagnosis had roughly a doubling of risk,” he said.