Very obese women have a 35% higher risk of developing triple-negative breast cancer and a 39% higher risk of estrogen receptor-positive breast cancer, scientists reported in Cancer Epidemiology, Biomarkers & Prevention. Physical inactivity was also associated with a higher chance of developing breast cancer. The authors say their findings hint at mechanisms beyond estrogen at play.
Triple-negative breast cancer is characterized by a lack of progesterone, estrogen and HER2 expression. Between ten to twenty per cent of all breast cancers of this type. Because of a lack of well effective medications, triple-negative breast cancer tends to have very poor outcomes.
Amanda Phipps, Ph.D., a postdoctoral fellow at the Fred Hutchinson Cancer Research Center, said:
"Breast cancer is not just one disease. It is a complex combination of many diseases. 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."
Scientists who study the patterns of health and illness and associated factors at the population level, epidemiologists, have long been aware of an association between obesity and postmenopausal breast cancer risk. We also know that greater physical activity reduces breast cancer risk. The authors explained that "A relationship between adipose tissue and estrogen is thought to contribute to this risk."
Phipps and team gathered information from 155,723 females who had enrolled in the Women's Health Initiative. Levels of baseline BMI (body mass index) and physical activity among 307 females who had had triple-negative breast cancer, as well as 2,610 who had estrogen receptor-positive breast cancer were assessed.
They found that:
- Those with the highest BMIs had a 35% higher chance of developing triple negative breast cancer
- Those with the highest BMIs had a 39% higher chance of developing estrogen receptor-positive breast cancer
- The most physically active women had a 23% lower risk of developing triple negative breast cancer
- Those with the highest levels of physical activity has a 15% lower risk of developing estrogen receptor-positive breast cancer
"The body of literature, primarily meta-analyses, has shown most of the risk between obesity and breast cancer to be among the estrogen receptor-positive subtypes. This paper raises questions about the possible role of growth factors or inflammation, but these will need to be explored with larger patient groups with known breast cancer subtypes, especially triple-negative breast cancers."
"Body Size, Physical Activity, and Risk of Triple-Negative and Estrogen Receptor-Positive Breast Cancer"
Amanda I. Phipps, Rowan T. Chlebowski, Ross Prentice, Anne McTiernan, Marcia L. Stefanick, Jean Wactawski-Wende, Lewis H. Kuller, Lucile L. Adams-Campbell, Dorothy Lane, Mara Vitolins, Geoffrey C. Kabat, Thomas E. Rohan9 and Christopher I. Li
Cancer Epidemiology, Biomarkers & Prevention
Published OnlineFirst March 1, 2011; doi: 10.1158/1055-9965.EPI-10-0974
Written by Christian Nordqvist