Well, when meats are cooked at a high temperature, they can produce chemicals called heterocyclic amines (which is carcinogenic). Char mark on meats are considered an area which contains a high concentration of HCA; that's why some people wrap their meats in foils and flip them frequently. In Malaysia, if you have heard about a Southeast Asian dish called satay, you would know that char spot is often inevitable and it is usually served with vegetables with high anti-oxidant properties (cucumber and probably some onions for example). I'm not sure if cucumber can reduce the chance of getting cancer but......