I'm not surprised, but it still amazes me. I have often comment that I didn't understand why, here in Australia, we have cancer warnings on cigarette packages but no similar requirement for alcohol.

The cancer.org[1] website has listed ethanol (drinking alcohol) as a Group A carcinogen for at least the past 8 years, if I recall correctly. You'll find it listed as 'Ethanol in alcoholic beverages' in [1].

The 'Alcohol and breast cancer'[2] entry on Wikipedia cites research that claims A study of 17,647 nurses found that high drinking levels more than doubled risk of breast cancer with 2% increase risk for each additional drink per week consumed. Binge drinking of 4–5 drinks increases the risk by 55%.

Another issue with ethanol consumption is that it's breakdown in the liver is rate limited by the enzyme alcohol dehydrogenase, which causes partial oxidation of ethanol to form acetaldehyde.[3] This rate limited pathway is probably why drinking fewer drinks (less than 1 per day and drinking it slowly) is less harmful.

1. http://www.cancer.org/cancer/cancercauses/othercarcinogens/g...

2. https://en.wikipedia.org/wiki/Alcohol_and_breast_cancer

3. https://en.wikipedia.org/wiki/Acetaldehyde