A new study suggests that weight loss could decrease the risk of endometrial cancer in postmenopausal women by as much as 29 to 56%. Researchers observed that the benefit was greatest for obese women who actively worked to lose weight. These findings, which draw from the Women's Health Initiative (WHI) study data, were published online in the Journal of Clinical Oncology.

"Many older adults think it's too late to benefit from weight loss, or think that because they are overweight or obese, the damage has already been done. But our findings show that's not true," said study author Juhua Luo, PhD, an associate professor of epidemiology and biostatistics at the Indiana University School of Public Health in Bloomington, Indiana. "It's never too late, and even moderate weight loss can make a big difference when it comes to cancer risk."

This study evaluated more than 35,000 women from the Women's Health Initiative (WHI) Observational Study, which enrolled postmenopausal women ages 50-79. Researchers measured participants' weight at the beginning of the study, and then again three years later to calculate change in body weight. Women who lost weight were also asked at this time whether their weight loss was voluntary or involuntary. Researchers then followed participants for more than 10 years on average to identify those who were diagnosed with endometrial cancer.

Women who intentionally lost weight saw a significant decrease in their risk of endometrial cancer compared to women whose weight remained stable. Specifically:

• Among women who lost 5% or more of their body weight after age 50, endometrial cancer risk was 29% lower, regardless of their age or how much weight they lost.
• The greatest reduction of endometrial cancer risk was found among women who were obese and voluntarily lost weight. Women who were obese and intentionally lost 5% or more of their body weight saw a 56% reduction in their risk.
• Furthermore, women who were overweight or obese and achieved a normal BMI after intentional weight loss had the same risk as women who maintained a stable, normal BMI.
• On the other hand, women who gained more than 10 pounds had a 26% higher risk of endometrial cancer.

"It's never too late to improve your health, and this study demonstrates losing weight's potential in reducing the risk for cancer," said Karen H. Lu, MD, chair of ASCO's Cancer Prevention Committee. "We hope these findings will encourage individuals who may be overweight to change their behaviors to reduce the amount of food eaten and increase their physical activity."

The authors also analyzed their findings to determine the influence of hormone use, as endometrial cancer is known to be highly hormone-related. However, the researchers found no significant difference in risk between women who used hormones and those who did not.

Many prior studies have shown that obesity increases the risk of endometrial cancer, but evidence on whether weight loss can reduce that risk is limited. According to the authors, this is one of the first studies to evaluate the effects of weight loss on cancer risk, and the first that measures actual change in weight rather than relying on patients' self-reported weight.

This study is also one of the first to distinguish whether participants' weight loss was intentional. Unintentional weight loss is usually associated with other comorbidities or illnesses, and these patients typically have poorer outcomes, which may affect the research findings.

"There have been more than a thousand studies linking obesity to an increased risk of endometrial and other cancers, but almost none that look at the relationship between weight loss and cancer risk" noted ASCO spokesperson Jennifer Ligibel, MD, an expert in cancer prevention.  "This study tells us that weight loss, even later in life, is linked to a lower risk of endometrial cancer. The findings also support the development of weight loss programs as part of a cancer prevention strategy in overweight and obese adults."

More studies are needed to determine whether these findings are generalizable beyond endometrial cancer. As such, the researchers are currently planning studies that will evaluate the effects of intentional weight loss on both cancer risk and mortality in other cancer types. The authors would also like to explore the role of weight loss in other populations, as this research was limited to older, postmenopausal women.

"We're interested to see whether weight loss plays a role in the prevention of other cancers that are linked to obesity," said Dr. Luo. "We already know that avoiding obesity is associated with many health benefits, but we do not know enough about the benefits of weight loss for adults who are already obese."

Endometrial cancer is the most common gynecologic cancer; more than 75% of cases occur in women age 55 and older.

The Women's Health Initiative program is funded by the National Heart, Lung, and Blood Institute; the National Institutes of Health; and the U.S. Department of Health and Human Services.