Hi Luis,
I just posted on the lymph system, which is related to the immune system. Check out the other post.
Again, the methods are found in Level II, to take care of physical blockages, or the practice of level I active and sm universe. this is the best way to proceed.
I recall once, Master Lin mentioning pumpkin as good food , perhaps once a week(?), for the immune system.
Foods, I think are nice reinforcements, supplements, lifestyle choices, to incorporate with,,,, 'also' practicing qigong, and/or using its given techniques for clearing yourself or friends. It is not the 'best', to come here for a quick specific/single technique, to then give a person, and effectively clear and balance their whole 'system'. Cancer, in general, has a list of do's and don't's relative to qigong wisdom. Again, there is alot of information to engage with, that can't be passed on in this format. Getting the courses are best.
love,
gallen