A new study has reported that an increase in cholesterol accelerates the development of mammary tumors and increases tumor aggressiveness in a mouse model of breast cancer. Diet and obesity are known to be important cancer risk factors. Many studies have reported a role for various individual nutrients in the initiation and progression of breast cancer. However, few studies have focused on the role of components of a Western diet. In the study, one group of mice prone to develop mammary tumors were given a diet containing 21.2% fat and 0.2% cholesterol, similar to typical Western diet. A control group of mice was fed a normal mouse diet with only 4.5% fat and almost no cholesterol.

Mice fed the higher cholesterol diet developed larger tumors that were faster growing and metastasized more easily compared to animals on the control diet. In addition, tumors of mice in the cholesterol group were more aggressive, and tumor angiogenesis (formation of blood vessels) was enhanced. The authors also examined the metabolism of cholesterol in the mice. Plasma cholesterol levels were observed to be reduced during tumor development but not prior to tumor initiation. This finding provides evidence for an increased use of cholesterol by tumors and for its role in tumor formation. In a separate interview, lead researcher Philippe G. Frank of the Department of Stem Cell Biology and Regenerative Medicine at Thomas Jefferson University said, "In a neighborhood, if you want to build more houses, you need more bricks. In tumors, cholesterol provides the bricks that are the foundation for further growth, and this cholesterol comes from the blood. A drop in blood cholesterol may signify that some tumors are growing as cholesterol provides support for breast cancer growth.