Modest Weight Loss Reduces Breast Cancer Risk

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Evidence of the numerous health benefits of weight loss continues to mount, and the hope is that doctors and patients are listening. A large observational study presented at the 2017 San Antonio Breast Cancer Symposium showed that weight loss of more than 5% is associated with a significantly lower incidence of breast cancer in postmenopausal women.1 This was true in overweight women and in those with stable weight.

“There was no significant difference between intentional and unintentional weight loss,” said lead author Rowan Chlebowski, MD, PhD, FASCO, of City of Hope National Medical Center, Duarte, California. “These findings suggest that interventions in postmenopausal women designed to generate weight loss may reduce cancer risk. The message is optimistic and important—even a modest weight loss can reduce the risk of breast cancer,” he stated. 

These findings suggest that interventions in postmenopausal women designed to generate weight loss may reduce cancer risk. The message is optimistic and important.
— Rowan Chlebowski, MD, PhD, FASCO

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“Obesity is recognized as a risk factor for breast cancer, but studies of weight loss and breast cancer provide inconsistent results. The current public health messages suggest that if you are overweight and obese, it may be too late to make a change,” Dr. Chlebowski continued.

The findings reported by Dr. Chlebowski were based on the Women’s Health Initiative Observational Study, which included 93,676 women treated at 40 clinical centers in the United States; of them, 61,335 were postmenopausal, with an anticipated 3-year survival and comprised the study population. 

The main objective of this analysis was to evaluate the association between weight change categories and breast cancer incidence. A secondary objective was to analyze the association between weight loss and breast cancer incidence by intentionality.

“We decided to use a 5% decrease in weight as a measurement, because it has been shown to reduce the frequency of diabetes and cancer,” Dr. Chlebowski said. “We used a tight window of weight change over a 3-year period.”

There were three categories of weight measurements: weight stable (± 5% weight gain); weight gain (≥ 5% gain); and weight loss (≥ 5% decrease). Incident breast cancer was documented at yearly contacts with patients. Weight change associations were examined in four subgroups defined by body mass index (overweight, obese, or normal), age group (50 years, < 70 years, or ≥ 70 years); race/ethnicity; and menopausal hormone therapy use.

Study Findings

Compared with women who had a stable weight, women with a 5% or greater weight loss were more likely to be younger, African American, and heavy smokers (P < .01 for all three categories). Women with a 5% or greater weight loss were more likely to have a higher body mass index but were less likely to be physically active or have used any menopausal hormone therapy (P < .01 for all). 

At baseline, the following factors were similar among weight-change groups: education, alcohol intake, history of treatment with estrogen alone or estrogen plus progestin, breast cancer risk score, bilateral oophorectomy, physical activity hours per week, body mass index, and diabetes.


  • Weight loss of 5% or more was associated with a reduced risk of breast cancer in a very large population-based study.
  • Risk reduction was similar for intentional and unintentional weight loss.
  • This is a message for primary care physicians, as well as oncologists.

Over a 3-year period, 41,139 women reported stable weight, 12,021 reported weight gain, 4,829 reported intentional weight loss, and 3,346 reported unintentional weight loss.

After a median follow-up of 11.4 years, women with a 5% or greater weight loss (n = 8,175) had a 12% lower breast cancer incidence, which was significant. This finding remained the same after adjusting for mammography frequency. Women who had a 5% or more weight gain did not have a higher overall incidence of breast cancer, but they did have a significantly higher incidence of triple-negative breast cancer (hazard ratio = 1.54, 95% confidence interval = 1.16–2.05).

No significant difference in breast cancer incidence was observed in women with weight loss related to whether weight loss was intentional or unintentional. ■


DISCLOSURE: Dr. Chlebowski reported no conflicts of interest.


1. Chlebowski RT, et al: Weight change in postmenopausal women and breast cancer risk in the Women’s Health Initiative observational study. 2017 San Antonio Breast Cancer Symposium. Abstract GS5-07. Presented December 8, 2017.

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