AHCC is a mushroom derivative as described, but it is also proof that one shouldn't tamper with natural substances. It has severe side effects.
Medicinal mushrooms have an excellent therapeutic effect without side effects or contra-indications, but only when used as a whole (although they should be hot water/ethanol extracted to be bioavailable).
AHCC is a proprietary product based on a natural product, and it has several severe side effects. Check online for a description of those.
Using a non-proprietary extract will have equal or even better effects (research for more info) without side effects, e.g., for those fighting cancer and the side effects of chemo.