Whether green tea by itself protects you from cancer is doubtful. It is very high in antioxidants, and eating a combination of foods that are high in different antioxidants do probably help protect cells. But every antioxidant tends to be protective of different parts of the body, so no one will protect you from all the different places cancer can break out. Don't put all your eggs in one basket, in short. The highest antioxidant form of green tea is a concentrate, so you might research that. White tea is probably higher in antioxidants than green, but not as easy to find. The rawer the tea the higher the nutritive content, basically, and so it goes white tea, green tea, and then the more processed middle teas popular in India and then the black tea popular in England and the US. The best green tea for drinking is to buy organic Japanese sencha (cha is the Chinese word for tea, in India it's chai). The macrobiotic quality teas are the best. The two companies easiest to find in the US are Great Eastern Sun (Haiku) and Choice. Now, if you shop in Japan, they have a ton that have devoted fans of taste, but if you're in the US you can find the two macrobiotic brands in any health food store and online easily and it's organic and will be nutritionally reliable. As to how much to drink, remember, it has caffeine. Although unlike coffee it also balanced with relaxants such as theanine, how much you want to consume will depend on your tolerance of caffeine. And again, there are concentrates available. The amount really depends on you and how strong you want it to be -- the more you use, the stronger it will be until you max out and have too much to brew. If you buy teabags you don't have to worry over this -- just brew the teabag. I doubt anyone knows how much to drink, as your body can only assimilate so much of anything during the day without just evacuating it, and if you drink ten cups a day, you will be spending quite a bit of time at the toilet evacuating. Rely more on a varied diet of colored vegetables, and fruits such as red grapes and blueberries and you will get an array of antioxidants. No one will do it alone. Peace.