Insulin resistance can increase risk of breast cancer in women

In a previous work the authors analyzed a large cohort of breast cancer patients to look whether an association existed between the risk of tumor development and the presence of the metabolic syndrome — a syndrome that predisposes to cardiovascular and other diseases, which is characterized by abdominal obesity, high levels of triglycerides and low concentrations of HDL cholesterol, increased blood pressure and insulin resistance. The authors indeed found an higher prevalence of metabolic syndrome among women affected by breast cancer in postmenopause compared to healthy women. In the new study the scientists confirm their previous findings and expand on by zooming in the contribution of insulin resistance.

When tissues become resistant to the action of insulin — which occurs often in obese people — a balancing mechanism further increases insulin production leading to a chronic hyperinsulinemia. Such high insulin levels can be detrimental to the body because insulin not only regulates glucose metabolism but has more functions such as stimulating cell proliferation and survival. Therefore the continuous activation of insulin pathways can contribute to cancer development by fuelling cancer cell growth. Consistently, by analyzing a cohort of 410 patients and 565 healthy women, the researchers found that 49% of patients were insulin resistant compared with 34% of controls indicating that insulin resistance can indeed increase the risk of developing breast cancer. Most of the insulin resistant patients were postmenopausal but, interestingly, most of them had fasting plasma glucose and/or fasting plasma levels in the normal range. It was only through the application of the homeostasis model assessment of insulin resistance (HOMA-IR) that the authors were able to identify a subset of patients with a subclinical insulin resistance but an increased cancer risk.

The HOMA-IR method takes into account both fasting plasma glucose and fasting plasma levels and is widely used in epidemiological studies to determine insulin resistance.

Overall these findings, obtained through the collaboration of the National Cancer Institute of Naples "Pascale Foundation", with the Sbarro Institute and the University of Siena, further support the hypothesis that metabolic syndrome, and particularly abdominal fat (waist circumference more than 88cm) and insulin resistance, can be considered risk factors for developing breast cancer after menopause. "Remarkably, HOMA-IR proves to be a promising tool for the identification of subclinical insulin resistance and to inform on breast cancer risk" says the leading author of the study, Immacolata Capasso, M.D. of the National Cancer Institute of Naples "Pascale Foundation", Italy. "Powerful tools for primary prevention are needed to help focusing the efforts on modifiable variables, such as life style habits including food and drink consumption and physical activity, and reduce the tumor burden" says Francesca Pentimalli, PhD, of the Center for Oncology Research of Mercogliano (CROM), Italy and coauthor of the study.