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By City of Hope | January 2, 2018
Chelbowski Bio Image Rowan Chlebowski, M.D., Ph.D.
Postmenopausal women who lose weight may have a significantly reduced chance of developing breast cancer, according to data presented by City of Hope’s Rowan Chlebowski, M.D., Ph.D., at the 2017 San Antonio Breast Cancer Symposium.
“Breast cancer is among the leading types of cancer and causes of death in American women,” said Chlebowski, a research professor in the Department of Medical Oncology & Therapeutics Research. “Obesity rates have been increasing in the United States. We wanted to determine if there was a link between obesity and breast cancer risk.”

Several studies have associated high body mass index (BMI) with increased breast cancer risk, noted Chlebowski. While this risk factor is largely preventable, it is estimated that more than 65 percent of American women are overweight or obese. 

We wanted to determine if weight loss was associated with lower breast cancer incidence, as studies have not been able to consistently show that losing weight reduces the risk of breast cancer,” said Chlebowski. 
Past studies have been limited to analyses with self-reported measurements, while the prospective study conducted by Chlebowski and colleagues utilizes a short-term, three-year period of measured body weight and height, followed by a long period of follow-up. 
Chlebowski and colleagues analyzed data from the Women’s Health Initiative (WHI) Observational Study. This program tracks the health of postmenopausal women between the ages of 50 and 79. Participants who had a normal mammogram, no prior breast cancer and were not underweight (BMI greater than 18.5) were eligible for enrollment in Chlebowski’s study. Measurements for height and weight were obtained upon enrollment, and measurements were reassessed three years following. 
At baseline, 41 percent of women were normal weight, 34 percent were overweight and 25 percent were obese. 
Of the 61,335 patients enrolled in Chlebowski’s study, 3,061 developed invasive breast cancer during an average of 11.4 years of follow-up. Compared to women with stable weight, those who lost weight (greater than 5 percent weight change) were 12 percent less likely to develop breast cancer following multivariable analysis. Weight loss of greater than 15 percent was associated with a 37 percent reduction in breast cancer risk.   
"In the three-year window of the study, relatively modest weight loss was associated with significant lowering of breast cancer incidence,” said Chlebowski.
From this study, we have evidence that a weight loss strategy can be effective in lowering breast cancer risk in postmenopausal women.”
This post was originally published by the American Association for Cancer Research and is reproduced with their permission.