Honestly I had never heard of a link between alcohol and cancer before.
For example, one article from 2011 mentions a link between alcohol and stomach cancer:
"If heavy drinking is a cause of stomach cancer, it may be related to one of the metabolic byproducts of alcohol -- called acetaldehyde. The substance is a known human carcinogen, Duell's team notes."
Note that this is related to heavy drinking. One glass of wine per week can be beneficial to your health, for example.
Liver cancer is also commonly known to be associated with alcoholics.
This is actually the fairly troubling reality of medical research in general. People who have financial interests in achieving particular conclusions have managed to weaponize these kinds of studies. There's a very real risk of important research getting lost in the tremendous amount of noise that's being generated.
Ethanol is a solvent, our brains are mostly fat - this should be a cause for concern. Cell walls are a phospholipid bilayer, which probably, at least partly, explains why ethanol is an irritant to our tissues. Anything that causes irritation over a long enough time can lead to an increase in cell turnover and inflammation. Anything that leads to an increased cell turnover and inflammation has the potential increase the risks of cancer.
Additionally, for all the supposed health benefits of drinking [whatever the fashionable number is this week] glasses of wine, all the experiments I've done by pouring wine on to plants and insects has led to a failure to thrive or death, whereas putting green leafy vegetables on a plant or insect typically leads to the organism thriving, or at worst disinterest.
Also, ethanol can be used as a toxic agent for the purposes of sterilisation. That doesn't sound like the sort of thing I would want to drink.
Additionally, even the organisms that produce alcohol for human consumption, the Saccharomyces yeast organisms, consider ethanol a waste product.
I'm not going to wait for conclusive evidence to prove that alcohol does or doesn't cause an increased risk of some types of cancer.
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...