Supplements, along with diet, are critical to support the immune system. If your immune system was not sick, there wouldn't be a cancer diagnosis. There is anti-cancer science behind each one shown. Be sure that you read the labels of your supplements. There are supplements being sold that contain fillers and toxic additives that are not safe for your body.
Keep in mind that supplements are just that -- they supplement diet, they cannot take the place of a good diet.
Warning: If you are taking any medication, please do your research to be sure that any supplement you take will not have any interaction or adverse effect on the body.