How Cholesterol Increases Breast Cancer Risk

Researchers at Duke Cancer Institute have found that a by-product of cholesterol acts like the hormone estrogen in women, helping breast cancer cells grow and spread. 

Breast cancer is one of the leading causes of death in the U.S.  Earlier research has linked genetics, hormones, stress and environmental toxins to the risk of breast cancer. The new study shows that a strong factor contributing to the cancer might be lurking in a Big Mac or even that tempting piece of cake.

Previous research has shown that high-fat diet is linked with an increased breast cancer risk. However, nobody knew how fat posed a threat. Now, researchers have found the cholesterol metabolite that mimics the hormone estrogen. The study may also explain why cholesterol-lowering drugs such as statins help reduce breast cancer risk.

"A lot of studies have shown a connection between obesity and breast cancer, and specifically that elevated cholesterol is associated with breast cancer risk, but no mechanism has been identified," said senior author Donald McDonnell, Ph.D., chair of the Department of Pharmacology and Cancer Biology at Duke, according to a news release. "What we have now found is a molecule - not cholesterol itself, but an abundant metabolite of cholesterol - called 27HC that mimics the hormone estrogen and can independently drive the growth of breast cancer."

Experts working with McDonnell had earlier found that the cholesterol metabolite 27-hydroxycholesterol - or 27HC worked like estrogen in animals. For their present study, they tested whether this by-product was sufficient for the cancer to grow and spread and if stopping it would reduce breast cancer risk.

Studies on mouse models showed that the metabolite was independently associated with breast cancer growth and progression. Also, mice given antiestrogen medication or drugs that stop the metabolite had lower breast cancer progression.

"This is a very significant finding," McDonnell said in a news release. "Human breast tumors, because they express this enzyme to make 27HC, are making an estrogen-like molecule that can promote the growth of the tumor. In essence, the tumors have developed a mechanism to use a different source of fuel."

Breast cancer is one of the most common cancers diagnosed in American women. Death rates due to the cancer have come down since 1990, but there has been an increase in the number of women diagnosed with the cancer. Health experts say that women can reduce their risk of developing the cancer by maintaining healthy weight, eating nutritious food and exercising.