dont rely on selenium alone. i have seen regressions without selenium, i have seen people take selenium without results. selenium will not hurt you, can always help, but should be included with a vast array of heavy minerals. It is most powerful as a preventative. Once you have an active tumor selenium should be part of a mixture of minerals. It can be toxic if taken too big of dose but usually stomach tolerance is an issue, Selenium's anti oxidant role against cancer is non existent. It's roll has been mistakenly reported using theory. Some lab analysis and some research indicate selenium protects against cancer but one must understand that all heavy minerals compete with potassium and that is how cancer eats. Potassium attached to glucose. Selenium also increase cellular and fluid oxygen retention, as does other heavy minerals.
So use selenium if you must but don't disregard other heavy minerals. dont forsake oxygen donors. push your selenium up to 200 mcg per day, taken in divided doses.