Obesity, Lack of Exercise Linked to Increased Risk of Triple Negative Breast Cancer
Obesity increases the risk of many health conditions, especially heart disease and diabetes. Being overweight is also linked to a higher risk of certain types of cancer. Researchers from the Fred Hutchinson Cancer Research Center have found that high body mass index (BMI) and low levels of physical activity are particularly associated with a particularly aggressive type of cancer known as triple-negative breast cancer.
Triple Negative Breast Cancer is Less Common, but Aggressive
"Breast cancer is not just one disease. It is a complex combination of many diseases," said Amanda Phipps, Ph.D., a postdoctoral fellow and lead researcher for the study. "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 subtypes of breast cancer are diagnosed based upon the presence of three receptors known to fuel most tumors. These are estrogen receptors, progesterone receptors, and human epidermal growth factor receptor 2 (HER2). In triple-negative breast cancer, none of these three receptors are found, making it a more difficult cancer to treat.
Of the 190,000 new cases of breast cancer diagnosed in the United States each year, about 10 to 20% are triple-negative. It is more prevalent among pre-menopausal and African-American women. It is a fast-growing cancer that has a higher risk of recurrence in the first three to five years after diagnosis.
Dr. Phipps and colleagues analyzed data from 155,723 women enrolled in the Women’s Health Initiative. Just over 300 had triple-negative breast cancer and 2,610 had ER+ (estrogen receptor-positive) breast cancer. The women were divided into four groups based on body mass index (BMI).
Women in the highest quartile for BMI had a 35% increased risk of developing triple-negative breast cancers compared to those in the lowest quartile. Though it is suspected that the relationship between adipose tissue and estrogen contributes to the increased risk of breast cancer overall, because triple-negative cancer is not fueled by estrogen, Phipps suggests another mechanism or pathway is involved.
Amy Trentham-Dietz PhD, an editorial board member of Cancer Epidemiology, Biomarkers and Prevention where the study findings are published, said “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.”
Physical activity appeared to reduce the risk of breast cancer. Women who reported having high levels of physical activity had a 23% decreased risk of triple-negative breast cancer and a 15% decrease risk of ER+ cancer.
"The results of this analysis suggest the existence of modest but modifiable risk factors for postmenopausal triple-negative breast cancer," the authors write. Trentham-Dietz agrees saying “avoiding obesity and staying active could lower a woman’s risk for all types of breast cancer.”
Amanda I. Phipps, Rowan T. Chlebowski, et al. Body Size, Physical Activity, and Risk of Triple-Negative and Estrogen Receptor–Positive Breast Cancer. Cancer Epidemiol Biomarkers, March 1, 2011 DOI: 10.1158/1055-9965.EPI-10-0974