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High body fat increases risk for breast cancer, regardless of BMI

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January 20, 2019

Postmenopausal women with normal BMI but relatively high body fat levels appeared to be at increased risk for invasive breast cancer, according to a study published in JAMA Oncology.

“It makes sense that if you have excess fat, you will also have increased inflammation and elevated cancer risk, even if BMI is normal,” Andrew Dannenberg, MD, director of cancer prevention at the Sandra and Edward Meyer Cancer Center at Weill Cornell Medicine, said in a press release. “We’ve shown that normal BMI is not an adequate proxy for risk of disease.”

In an ad hoc secondary analysis of data from the Women’s Health Initiative, Dannenberg and colleagues assessed 3,460 postmenopausal women (mean age, 63.6 years; range 50-75 years) with BMIs ranging from 18.5 mg/kg2 to 24.9 mg/kg2.

Women completed self-administered questionnaires at baseline on demographic characteristics, menstrual history, medical history and diet/lifestyle factors.

Researchers measured body fat at baseline and years 1, 3, 6 and 9 using dual-energy X-ray absorptiometry (DXA). Subsets of women also underwent blood tests to check for inflammatory and metabolic changes associated with obesity and breast cancer risk.

Median follow-up was 16 years (range, 9-20).

Follow-up finished in September 2016, by which time 182 primary invasive breast cancer cases had been identified in women with normal weight and DXA measurements; 146 of these were ER positive.
found that women with the highest body fat totals had a nearly doubled risk for breast cancer, including ER-positive disease, compared with those with the lowest body fat totals.

Among women in the highest quartile of whole-body fat, multivariable-adjusted HRs were 1.89 (95% CI, 1.21-2.95) for invasive breast cancer and 2.21 (95% CI, 1.23-3.67) for ER-positive breast cancer.

For women in the highest quartile of trunk fat mass — defined by the fat in the torso apart from head and limbs — HRs were 1.88 (95% CI, 1.18-2.98) for invasive breast cancer and 1.98 (95% CI, 1.18-3.31) for ER-positive disease.

Time-dependent covariate analyses showed similar positive associations for serial body fat measurements.

Women in the highest quartiles of trunk fat mass had higher circulating levels of insulin, C-reactive protein, interleukin 6, leptin and triglycerides, but lower levels of high-density lipoprotein cholesterol and sex hormone-binding globulin, than those in the lowest trunk fat mass quartiles.

These findings reveal the importance of measuring body fat in addition to BMI, Isabel Pimentel, MD, of the division of medical oncology and hematology in the department of medicine at Lunenfeld-Tanenbaum Research Institute and Mount Sinai Hospital, and colleagues wrote in a related editorial.

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“The results reported by Iyengar [and colleagues] highlight the importance of research differentiating the contributions of body size, body composition and metabolic profiles to breast cancer risk,” Pimentel wrote. “Better understanding of these issues may lead to novel preventive strategies, and may have relevance rot the treatment of women diagnosed with breast cancer.” – by Jennifer Byrne

Disclosure s : The researchers report no relevant financial disclosures. Pimentel and colleagues report no relevant financial disclosures.

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