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Weight loss lowers risk for postmenopausal breast cancer

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October 8, 2018

Photo of Rowan Chlebowski
Rowan T. Chlebowski

Postmenopausal women who lost weight over 3 years demonstrated a 12% decreased risk for breast cancer compared with women whose weight remained stable, according to an observational study published in Cancer.

“Obesity is associated with increased risk of incident postmenopausal breast cancer,” Rowan T. Chlebowski, MD, PhD, researcher professor in the department of medical oncology and therapeutics research at City of Hope National Medical Center, and colleagues wrote. “Because approximately one-third of postmenopausal women in the United States are obese, obesity represents a common and potentially modifiable factor related to breast cancer outcome. However, it has not been established that weight loss in postmenopausal women decreases breast cancer incidence or breast cancer mortality.”

Chlebowski and colleagues used data from the Women’s Health Initiative Observational Study to assess associations between weight loss and postmenopausal breast cancer.

The analysis included 61,335 postmenopausal women with no prior breast cancer and normal mammograms. Researchers evaluated body weight, height and BMI at baseline and at year 3.

Researchers categorized weight change as stable (change of less than 5%; n = 41,139), loss of 5% or more (n = 8,175) or gain of 5% or more (n = 12,021).

During a mean follow-up of 11.4 years, researchers observed 3,061 cases of breast cancer.

Mean time from 3-year weight determination to breast cancer diagnosis was 6.47 years (range, 0.005-17).

Women with weight loss had a significantly lower risk for breast cancer compared with women whose weight remained stable (HR = 0.88; 95% CI, 0.78-0.98).

The association remained after adjustment for mammography (HR = 0.88; 95% CI, 0.78-0.99) and when self-reported intentionality of weight loss was considered.

Weight gain of 5% or more did not appear associated with breast cancer risk (HR = 1.02; 95% CI, 0.93-1.11). However, researchers did observe an increased risk for triple-negative breast cancer among those with weight gain (HR = 1.54; 95% CI, 1.16-2.05).

“Our study indicates that moderate, relatively short-term weight reduction was associated with a statistically significant reduction in breast cancer risk for postmenopausal women,” Chlebowski said in a press release. “These are observational results, but they are also supported by randomized clinical trial evidence from the Women’s Health Initiative Dietary Modification trial where, in a randomized clinical trial setting, adopting a low-fat dietary pattern that was associated with a similar magnitude of weight loss resulted in a significant improvement in breast cancer overall survival. These findings, taken together, provide strong correlative evidence that a modest weight-loss program can impact breast cancer.”

Study limitations included weight measurement at baseline and year 3 only and the lack of biological rationale for the association between weight gain and breast cancer. – by Cassie Homer

Disclosures: Chlebowski reports consultant roles with AstraZeneca, Novartis and Pfizer. The other authors report no relevant financial disclosures.