Postmenopausal women who lost even a modest amount of weight were significantly less likely to develop breast cancer, researchers reported last week at the San Antonio Breast Cancer Symposium. Gaining weight, however, did not increase the overall risk.
“From this study, we have evidence that a weight loss strategy can be effective in lowering breast cancer risk in postmenopausal women,” said researcher Rowan Chlebowski, MD, PhD, of City of Hope National Medical Center in Duarte, California.
A number of epidemiological studies have seen a link between being overweight or obese and increased likelihood of developing cancer. According to a recent report from the Centers for Disease Control and Prevention, overweight people are at higher risk for at least 13 different types of cancer, which together make up about 40 percent of all cancer diagnoses in the United States. Breast cancer among postmenopausal women is one of them. But so far, it has been difficult to show whether weight loss lowers cancer risk, according to Chlebowski.
Chlebowski’s team sought to learn more about the influence of weight change on invasive breast cancer risk among postmenopausal women. They analyzed data from more than 61,000 participants in the Women’s Health Initiative Observational Study, part of a long-term national health study focused on strategies for preventing heart disease, breast and colon cancer and bone fractures among women ages 50 to 79.
Participants were enrolled at 40 clinical centers in the United States between 1993 and 1998. They had no prior history of breast cancer, had normal mammograms and were not underweight. At study entry, 41 percent of the women were classified as normal weight, 34 percent were overweight and 25 percent were obese.
In this prospective study, height and weight were measured at enrollment and again three years later, and the women were asked whether they intended to lose weight. Prior studies of the link between cancer and weight have generally relied on self-reported weight changes, Chlebowski noted.
Weight change was categorized as stable (41,139 women); a gain of 5 percent or more (12,021); or a loss of at least 5 percent (8,175 women). The average gain and average loss were both around 18.5 pounds. About 60 percent of those who lost weight said they did so intentionally. Women who gained weight were younger, heavier smokers and more likely to be Black. Surprisingly, women who lost weight were less likely to be physically active.
Over 11 years of follow-up, a total of 3,061 women developed invasive breast cancer, Chlebowski reported.
The researchers found that women who lost at least 5 percent of their body weight had a 12 percent lower risk of developing breast cancer compared with those who maintained a stable weight. Women who lost 15 percent or more of their baseline weight had a 37 percent lower likelihood of developing breast cancer. The difference was statistically significant, meaning it was probably not attributable to chance. It did not matter whether women said they had intended to lose the weight or not.
Conversely, women who had a weight gain of 5 percent or more did not have a higher risk of breast cancer overall. However, they did have a 54 percent higher risk of developing triple negative breast cancer. This type of cancer does not have hormone receptors or HER2 receptors and is harder to treat.
These findings are important, Chlebowski suggested, because they offer women a proactive way to reduce their risk of developing cancer risk.
C. Kent Osborne, MD, of the Dan L. Duncan Cancer Center at Baylor College of Medicine in Houston, who moderated a press briefing about the study, said it was important that these results be communicated to general practitioners, not just to oncologists.
Click here to read the study abstract.
Click here to read a press release about the study.