A consult is an excellent idea, and as soon as possible. Hopefully this will turn out NOT to be cancer, but it's not worth taking the risk of not checking it out.
There are other conditions that present at least some of these signs and symptoms. Has anyone talked about the possibility of lupus erythematosis? Have they tested him for Lyme's disease? Sometimes a person can have several things going on at once - one illness kind of tends to hide and confuse diagnosis of the other. That is a possibility with your son, also.
More comprehensive testing might be indicated - possibly a total body scan.
Keep pressuring the docs for an answer. Don't settle for any "let's wait and see" answer. I know that seeing more drs, having more tests, getting more blood drawn, etc, is not any fun for your little boy, but pushing for answers is what you must do if he is to perhaps someday have a normal life.
I wish you and your son and family the best. Please let us know what you find out, so that we can either continue to offer you support, or all do the happy dance if it is diagnosed as something more benign.
Sincerely,
Tre