Two Drinks A Day Increases Breast Cancer Risk By 32%

A beerEven relatively low levels of alcohol consumption may increase a womens risk of developing one form of breast cancer by a significant amount according to a recent American study of almost 200,000 women.

The research, conducted by the National Cancer Institute looked at data from 184,418 women in order to explore the link between breast cancer and alcohol consumption. During an average follow up period of 7 years, 5,461 women developed breast cancer with 70% of the women in the study reporting some alcohol consumption during the study. The researchers found that alcohol consumption was associated with an increase in a particular type of breast cancer called ER+/PR+ where both estrogen receptors and progesterone receptors are over expressed.

This form of cancer was found to be 7% more likely in women who consumed less than one drink a day compared to those who did not consume alcohol. Those who consumed between one and two standard drinks a day were 32% more likely to develop breast cancer and those who consumed three or more standard drinks a day were 51% more likely to develop breast cancer. The increased risks remained the same regardless of whether the women consumed beer, wine, or spirits.

The researchers found alcohol consumption also increased the risk of the relatively rare ER+/PR- form of breast cancer where only estrogen receptors are over expressed. Alcohol consumption was not associated with an increased risk of developing ER-/PR- breast cancer where neither of the receptors are over expressed.

Around 70% of all breast cancer cases show over expression of estrogen receptors with ER+/PR+ the most common form of breast cancer in women. It is thought that over expression of estrogen receptors is linked to breast cancer by two mechanisms. First estrogen receptors are thought to stimulate the growth and replication of mammary cells which are found in the breast. Increased replication of cells increases the chances of a cancer causing mutation occurring. Secondly estrogen receptor over expression increases estrogen metabolism. One of the metabolic pathways by which estrogen is broken down is known to result in several cancer causing products.

The researchers believe that alcohol interferes with the metabolism of estrogen, which in turn leads to an increased risk of estrogen sensitive breast cancer.

The research is to be presented at the 2008 annual meeting of the American Association for Cancer Research which is held between April 12 and 16 in San Diego.