An item in Chemistry in Britain Feb. 1999 reports the finding of a team of Japanese researchers (J. Agric. Food Chem. 1999, 47(1), 221).
They've found that a wide range of alcoholic drinks, including lager, bitter, stout, wine, brandy and sake, can inhibit the activity of certain suspected cancer-causing substances: heterocyclic amines, present in cooked foods.
Stout appears to be the most effective whereas whiskey, non-alcoholic beer and pure alcohol had no effect.
The exact mechanism involved isn't clear (there may be several) but an extract of hops also showed an effect, suggesting that the key agent may be of plant origin.