Obesity, inactivity may increase risk of breast cancers

New findings published online March 1 in Cancer Epidemiology, Biomarkers & Prevention confirm the risk of breast cancer among obese and inactive women and suggests additional mechanisms beyond estrogen.
 
Women’s Health Initiative researchers found a relationship between obesity, physical activity and triple-negative breast cancer, a subtype of breast cancer characterized by a lack of estrogen, progesterone and HER2 expression. Triple-negative breast cancers account for about 10 percent to 20 percent of all breast cancers and are associated with an extremely poor prognosis due to a lack of targeted drug therapies.

Known risk factors increase for rare cancer

“Breast cancer is not just one disease. It is a complex combination of many diseases,” said Dr. Amanda Phipps, a postdoctoral fellow in the Hutchinson Center's Public Health Sciences Division. “The fact that we found an association with triple-negative breast cancer is unique because, biologically, this subtype is very different from other breast cancers.” The study marks Phipps’ second recent finding pertaining to triple-negative breast cancer. In the Feb. 23 Journal of the National Cancer Institute, Phipps linked multiple births with increased risk of the rare cancer.

BMI, estrogen connection

Epidemiologists have long noted a link between obesity and increased risk of postmenopausal breast cancer, as well as a decreased risk that comes with greater physical activity. A relationship between body fat and estrogen is thought to contribute to this risk.

Phipps and colleagues, including Drs. Ross Prentice, Anne McTiernan, and Chris Li of PHS, analyzed data from the 155,723 women enrolled in the Women’s Health Initiative. They assessed levels of baseline body mass index and recreational physical activity among the 307 women who had triple-negative breast cancer and the 2,610 women who had estrogen receptor-positive breast cancer.

Results showed that women with the highest BMI had a 35 percent increased risk of triple-negative breast cancers and a 39 percent increased risk of estrogen receptor-positive breast cancers. Those who reported high rates of physical activity had a 23 percent decreased risk of triple-negative breast cancer and a 15 percent decreased risk of estrogen receptor-positive breast cancer.

[Adapted from an American Association for Cancer Research news release]