Weight loss reduces breast cancer risk for postmenopausal women
SAN ANTONIO — A 5% weight loss reduced risk for breast cancer among a large cohort of postmenopausal women, according to study results presented at the San Antonio Breast Cancer Symposium.
Although obesity is an established risk factor for postmenopausal breast cancer, studies of the benefit of weight loss regarding breast cancer risk have provided inconsistent results, according to Rowan T. Chlebowski, MD, PhD, chief and professor-in-residence in medical oncology/hematology at David Geffen School of Medicine at UCLA.
Current public health messaging for women at risk for breast cancer is limited to “avoid body fatness,” Chlebowski said. “This suggests that if you’re overweight or obese, it’s too late to make a change to show benefit.”
Thus, Chlebowski and colleagues evaluated associations between weight change categories and breast cancer incidence among 61,335 postmenopausal women aged 50 to 79 years from the Women’s Health Initiative Observational Study. The study — conducted between 1993 and 1998 — had a mean follow-up duration of 11.4 years.
“There was no [study] intervention,” Chlebowski said. “We were watching these women as they go on their normal daily activities.”
Researchers also explored the association between weight loss and breast cancer incidence by weight loss intentionality as a secondary analysis.
The analysis considered three weight categories: stable, 5% increase or 5% decrease.
“We looked at the 5% decrease, because this level has been shown to change some biochemical markers potentially associated with cancer and reduce the frequency of diabetes,” Chlebowski said.
Patients provided height, weight and BMI measurements at baseline. Researchers asked patients if they gained or lost weight at year 3 — which Chlebowski described as a “tight window” of change — and whether the weight change was intentional or unintentional.
Compared with women with stable weight, women who had a 5% weight gain tended to be younger, black and heavy smokers (P < .01 for all).
Women with a greater than 5% weight loss had a higher BMI, were less likely to have used menopausal hormone therapy and were less physically active (P < .01 for all), which “is a paradox,” Chlebowski said. He noted that this group had a BMI of 29.9 kg/m2, which made the researchers wonder whether their overweight was the motivating factor for their loss.
During follow-up, 3,061 women developed invasive breast cancer.
Results of a multivariable adjusted analysis showed that, compared with 41,139 women with stable weight, the 8,175 women with a 5% decrease in weight had significantly lower breast cancer risk (HR = 0.88; 95% CI, 0.78-0.98). The trend persisted in an analysis that adjusted for mammography (HR = 0.88; 95% CI, 0.78-0.99).
The 12,021 women who gained weight did not have an overall increase in breast cancer risk (HR = 1.02; 95% CI, 0.93-1.11).
“There was an increase in triple-negative breast cancer, which we don’t have a good explanation for,” Chlebowski said, noting an HR of 1.54 (95% CI, 1.16-2.05) in this group.
Other findings showed no significant difference in breast cancer risk among women who lost weight intentionally (HR = 0.91; 95% CI, 0.79-1.04) or unintentionally (HR = 0.82; 95% CI, 0.68-0.99).
“These findings suggest that weight loss interventions in postmenopausal women may reduce breast cancer risk,” Chlebowski concluded. “These are very optimistic findings in that they provide a lesson to postmenopausal women — even a modest weight loss may provide a health benefit. This is a relatively new finding that should have public health implications.” – by Rob Volansky
Chlebowski, et al. Abstract GS5-07. Presented at: San Antonio Breast Cancer Symposium; Dec. 5-9, 2017; San Antonio.
Disclosures: Chlebowski reports consultant fees from AstraZeneca, Genentech, Novartis and Pfizer. Please see the abstract for all other authors’ relevant financial disclosures.