Postmenopausal women who are metabolically healthy but overweight do not have the same increased risk of breast cancer as those who are overweight with high insulin levels, one of the first studies to examine the association between insulin and breast cancer has found.

These results suggest that the homeostasis model assessment of insulin resistance (HOMA-IR) or fasting insulin levels “may be useful in combination with other predictors of breast cancer risk in efforts to individualize breast cancer screening practices,” wrote Marc Gunter, of the Department of Epidemiology and Biostatistics in the School of Public Health, Imperial College in London, UK, and colleagues in Cancer Research.

“There is emerging evidence that diabetes and prediabetic states are associated with various cancers, including breast cancer, in postmenopausal women, and there are ongoing studies and trials to investigate the efficacy of anti-diabetic drugs, such as metformin, on outcomes in breast cancer patients,” Dr. Gunter told Cancer Therapy Advisor.

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“The findings of our study further support this link and we can expect to see more studies investigating diabetes, metabolic health, and cancer outcomes in coming years.”

Using data from 497 incident breast cancer cases and a subcohort of 2,830 from the Women’s Health Initiative, the investigators compared risk of incident postmenopausal breast cancer among metabolically healthy normal weight women, defined as a body mass index (BMI) of 18 kg/m2 to 24.9 kg/m2, with a HOMA-IR in the first quartile (normal insulin sensitivity), with women who were metabolically unhealthy and overweight (25 kg/m2 or more) or metabolically unhealthy and normal weight.

RELATED: Insulin Resistance Raises Breast Cancer Risk Regardless of Weight

Because of the mitogenic/antiapoptotic activity of insulin, high levels in overweight women may explain the link to increased risk of breast cancer in postmenopausal women.

The study found that metabolically healthy overweight women were not at elevated risk of breast cancer compared with metabolically healthy normal weight women.