Hi Just read your sons history etc and I think personally, (a mum of 2 boys) follow your instint. Go for a 2nd, 3rd, 4th opinion and dont stop still your satisified. I feel for you and your family. My mum has cancer and I understand your fears. Try talking on Oncochat IRC channel. There r loads of people their like me who can talk to you online.
Thinking of you, your son, and family
mandy xxx