Expert Point of View: Neil M. Iyengar, MD

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Neil M. Iyengar, MD, Assistant Attending Physician at Memorial Sloan Kettering Cancer Center, New York, has researched the links between breast cancer and lifestyle. He provided comments on these two abstracts from the 2020 San Antonio Breast Cancer Symposium (SABCS) for The ASCO Post.

“These two studies presented at SABCS provide important observations that support the growing body of evidence linking metabolic health to breast cancer risk and outcomes,” Dr. Iyengar said. “The findings further demonstrate the need for dietary and other lifestyle interventions that optimize metabolic health to improve breast cancer risk and outcomes.”

According to Dr. Iyengar, it is now well established that obesity is associated with an increased risk for postmenopausal hormone receptor–positive breast cancer and shortened survival after breast cancer diagnosis. Generally, any lifestyle pattern that contributes to obesity could therefore increase the risk of breast cancer incidence and mortality, he noted.

Neil M. Iyengar, MD

Neil M. Iyengar, MD

Newer Evidence: Beyond Obesity

“However, newer evidence suggests that metabolic factors such as insulin signaling and the health of the adipose tissue can contribute to breast cancer risk and outcomes independent of classical obesity (which is defined by elevated body mass index),” Dr. Iyengar continued. “For example, our group reported that a higher body fat level in normal-weight, nonobese women is associated with more than a twofold increase in the risk of invasive breast cancer after menopause.1 We have also reported that dysfunctional and inflamed breast adipose tissue is associated with features of the metabolic syndrome, greater in-breast expression of aromatase, and an increased risk of breast cancer recurrence.2,3 Although inflamed breast fat is present in the majority of overweight and obese individuals, it is also present in up to one-third of normal-weight women.”

“In light of these biologic findings, data linking lifestyle patterns such as diet to breast cancer risk and outcomes are critical to the development of effective intervention strategies,” he emphasized.

Two Studies Show Dietary Pattern

The findings from the Nurses’ Health Study and the NutriNet-Santé cohort showed that a dietary pattern known to disrupt metabolic health by increasing insulin levels and lowering insulin sensitivity is associated with increased breast cancer risk and mortality. These findings are important, commented Dr. Iyengar, as they suggest that interventions to reverse this dietary pattern (eg, a low-glycemic diet or a diet that prevents diabetes [diabetes risk-reduction diet]) should be studied for their impact on reducing breast cancer risk and improving survival after diagnosis. Several ongoing clinical trials are testing these interventions now, he indicated. 

DISCLOSURE: Dr. Iyengar has received honoraria from Novartis; served as a consultant or advisor to Seattle Genetics and Novartis; and received institutional research funding from the Breast Cancer Research Foundation, the National Cancer Institute, the American Cancer Society, and Conquer Cancer, the ASCO Foundation.


1. Iyengar NM, Arthur R, Manson JE, et al: Association of body fat and risk of breast cancer in postmenopausal women with normal body mass index: A secondary analysis of a randomized clinical trial and observational study. JAMA Oncol 5:155-163, 2019.

2. Iyengar NM, Zhou XK, Gucalp A, et al: Systemic correlates of white adipose inflammation in early-stage breast cancer. Clin Cancer Res 22:2283-2289, 2016.

3. Iyengar NM, Brown KA, Zhou XK, et al: Metabolic obesity, adipose inflammation and elevated breast aromatase in women with normal body mass index. Cancer Prev Res (Phila) 10:235-243, 2017.


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