Welcome to the site. I am very sorry to hear about your son, as Mary says, he is so young and I am sorry that you had to find us all. I can't help you with your question regarding maitake mushrooms, but I just wanted to stop by and welcome you here. If you use the search function at the top of the page you might find other posts regarding maitake mushrooms from our members.
I hope that you will keep coming back here as you will get so much support from us all here. And please feel free to ask a ton of questions and we will all help if we can. I will keep my fingers crossed for the best possible outcome for your son with his gem/cis combo.
My best wishes to you and your son,
Any advice or comments I give are based on personal experiences and knowledge and are my opinions only, they are not to be substituted for professional medical advice. Please seek professional advice from a qualified doctor or medical professional.