Study: How Obesity May Trigger Certain Breast Cancers

AICR’s expert report and its updates have found that excess body fat increases the risk of developing breast cancer in postmenopausal women.  As scientists are learning, how excess body fat plays a role in breast cancer varies by cancer type.

In a study published last month in the journal Cancer Prevention Research, scientists looked at the role excess body fat plays in the development of two types of triple-negative breast cancers. These types of breast tumors don’t respond to hormones and growth factors that typically fuel less aggressive types of breast cancer.

One of the changes that occurs in these two types of breast cancers is EMT, or epithelial mesenchymal transition. EMT signals early development of cancer in epithelial cells, the cells that line the breasts and other organs. It is recognized as a feature of many aggressive tumors.

Epithelial cells typically have a “top” and a “bottom.”  The bottom is anchored to what is referred to as a basement membrane to keep it in place for normal functioning. Mesenchymal cells, on the other hand, tend to be more mobile, invasive, and resistant to programmed cell death.

Several proteins, enzymes, and microRNAs can initiate the transition from an epithelial to a mesenchymal type cell, which can then migrate to other sites in the body.  Cancer cells undergoing EMT can invade nearby tissues and are often resistant to chemotherapies.

In the study, researchers divided mice into three groups and fed them a high calorie diet, a low calorie diet, or a control diet to see what effect caloric intake had on the development of EMT.  After eight weeks on the diets, the mice fed the high calorie diet became obese and the mice fed the calorie-restricted diet became thin. The mice were then exposed to cancer cells.

Six weeks later, researchers monitored the mice for tumor development.  They discovered that caloric intake impacted the progression of these two aggressive types of breast cancer.  Compared to the control group, tumors were more developed in the obese mice and smaller in the slender mice. In addition, several cancer-promoting factors such as hormones, growth factors, and proteins that trigger inflammation were more abundant in breast cancer tumors in the obese mice but not the thin mice.

Their findings suggested that diet-induced obesity creates an environment that is conducive to EMT but calorie restriction discourages it.

Nearly one third of women living in the US are overweight or obese. To learn more about the role that obesity plays in cancer risk, visit here.

Teresa L. Johnson, MSPH, RD, is a nutrition and health communications consultant with a long-time interest in the intersection of nutrition, exercise, and wellness.


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