Insulin Resistance Tied to Higher Breast Cancer Incidence in Postmenopausal Women

Aside from skin cancers, breast cancer is the most commonly diagnosed cancer among women. It is the second leading cause of cancer-related deaths among women (coming second to lung cancer). Identifying risk factors for breast cancer and associated mortality may help reduce this risk. A new study found that postmenopausal women with insulin resistance may be at a higher risk of contracting and breast cancer.

“Insulin resistance is associated with higher all‐cause and cancer‐specific mortality in postmenopausal women. However, to the authors’ knowledge, information regarding insulin resistance and breast cancer mortality risk is limited. Therefore, the authors examined associations between insulin resistance and breast cancer incidence and mortality in a subsample of Women’s Health Initiative participants,” wrote the researchers.

The study included 22,837 postmenopausal women whose fasting baseline glucose and insulin levels data were available. Women were followed for breast cancer and associated mortality; medical record review and serial National Death Index linkage–enhanced mortality findings were use to confirm breast cancer incidence. The primary outcomes were breast cancer incidence, deaths from breast cancer, and deaths from any cause after breast cancer.

Median follow-up was 19.8 years, during which time there were 1,328 breast cancer cases. A total of 512 deaths were reported, of which 151 were attributed to breast cancer. Women in the highest homeostatic model assessment of insulin resistance (HOMA‐IR) quartile had a higher incidence of breast cancer (hazard ratio [HR], 1.34; 95% confidence interval [CI], 1.12 to 1.61; P for trend = 0.003). HOMA-IR was not associated with risk of death from breast cancer (HR, 1.04; 95% CI, 0.60 to 1.79), but women in the highest HOMA-IR quartile, compared to those in the lowest quartile, had an increased risk of death after breast cancer (HR, 1.78; 95% CI, 1.32 to 2.39; P for trend < 0.001).

The study was published in the journal Cancer.

Are Breast Cancer Death Rates On the Decline?

Although breast cancer death rates are on the decline in the U.S., the rate of which they are declining has decreased, according to a previous study.

The breast cancer death rate declined by 40% from 1989 to 2017. Though this death rate continues to decrease, it is doing so at a slower rate in recent years. From 1998 to 2011, breast cancer mortality in women dropped by 1.9%, but only decreased by 1.3% from 2011 to 2017. Of note, despite the consistent decline in breast cancer death rates, the incidence rate has been slowly increasing by 0.3% every year since 2004.