Newly published study reveals differing effects of obesity and metabolic syndrome on breast cancer

Both obesity and metabolic syndrome – a cluster of conditions like high blood pressure and high blood sugar – increase the risk of breast cancer, but in differing ways for different subtypes of the cancer. A University of Oklahoma researcher helped to lead a national study that produced those results, which may help physicians better care for patients at higher risk for breast cancer.

The study is from the Women’s Health Initiative (WHI), an effort that began in the early 1990s and continues to yield valuable data about postmenopausal women’s risks for cancer, cardiovascular disease, osteoporosis and other conditions. The initiative, funded by the National Heart, Blood and Lung Institute, a component of the National Institutes of Health, is the largest women’s health prevention study ever conducted.

Robert Wild, M.D., Ph.D., a professor of obstetrics and gynecology in the OU College of Medicine, has been involved with the WHI since its beginning and is a co-author of the latest study, published in Cancer, a journal of the American Cancer Society. The research followed another WHI study showing that women who ate a low-fat diet for about eight years decreased their risk of dying from breast cancer by 21% over the next 20 years. Those findings led researchers to consider whether the reduced risk was related to a decrease in obesity or an improvement in the conditions associated with metabolic syndrome. As it turns out, the answer is both.

“This study shows that obesity had an effect on breast cancer independent of metabolic syndrome, and that metabolic syndrome had an effect on breast cancer independent of obesity,” Wild said. “And they affected various subtypes in different ways, which influenced whether women were diagnosed with breast cancer and whether they died from it.”

The upshot of the study is simpler: Keeping both waist circumference and metabolic conditions under control is important to reduce the risk of being diagnosed with breast cancer and the risk of dying from it.

“This study is essentially saying to get back to the basics,” he said. “Prevention is important, and we need to be paying attention to both metabolic syndrome and weight.” Metabolic syndrome includes increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglycerides (a type of fat in the blood), all of which also increase the risk for cardiovascular disease and diabetes.

More specifically, the study found that:

• Metabolic syndrome is significantly associated with 53% more deaths after breast cancer and a 44% higher breast cancer mortality (the proportion of a population that dies).
• Metabolic syndrome is also associated with poor prognosis in two specific types of breast cancer: estrogen receptor (ER)-positive and progesterone receptor (PR)-negative.
  • ER-positive breast cancer occurs when high levels of estrogen in the breast cancer cells help the cancer grow and spread. This type of cancer represents 70-80% of all breast cancer diagnoses and typically responds well to hormone therapy, which blocks hormones like estrogen.
  • PR-negative breast cancer means the cancer has no hormone receptors and therefore does not respond to hormone therapy. It also tends to grow faster than hormone-positive cancers.
• Obesity status is significantly associated with more total breast cancers and more deaths after breast cancer, with higher mortality only in women with severe obesity.
• Obesity status is also associated with good prognosis in ER-positive and PR-positive cancers. Both can be treated with hormone therapy and tend to grow more slowly than those that are hormone receptor-negative.

Including this latest study, Wild has been a co-author on dozens of previous publications using data from the more than 161,000 women enrolled in various WHI studies.

“The Women’s Health Initiative is the gift that keeps on giving,” Wild said. “It is a great opportunity to make use of quality information. In the beginning, I don’t think we knew what a valuable resource it would still be years later.”

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About the project

Read the full publication, titled “Breast cancer incidence and mortality by metabolic syndrome and obesity: The Women’s Health Initiative,” at https://doi.org/10.1002/cncr.35318

About the University of Oklahoma

Founded in 1890, the University of Oklahoma is a public research university located in Norman, Oklahoma. As the state’s flagship university, OU serves the educational, cultural, economic and health care needs of the state, region and nation. OU was named the state’s highest-ranking university in U.S. News & World Report’s most recent Best Colleges list. For more information about the university, visit www.ou.edu.