PSK and PSP, the two protein-bound polysaccharides
Turkey tail (Trametes versicolor, also called Coriolus) is the source of two well-characterised protein-bound polysaccharides: polysaccharide-K (PSK, marketed in Japan as krestin) and polysaccharopeptide (PSP). Both are beta-glucan complexes that interact with the innate immune system, and they are among the few medicinal-mushroom compounds with substantial clinical study behind them rather than only laboratory data.
Adjunctive use, not a standalone treatment
Mechanistically these compounds are described as training or priming innate immunity, engaging receptors on macrophages and natural killer cells that recognise fungal glucans. In Japan PSK has been used for decades as an adjunctive agent alongside conventional chemotherapy for certain cancers, with some trials suggesting survival benefit in specific settings. The key word is adjunctive: it is given with standard treatment, not instead of it.
Turkey tail is not an approved cancer cure outside that adjunctive context and should never replace oncology care. This is general educational information, not medical advice; cancer decisions belong with a qualified oncologist.