If you're from Japan, you're probably wondering why I've listed PSK under alternative therapies. In Japan, PSK is an approved anti-cancer drug with 20 years of research behind it. PSK sales in Japan account for hundreds of millions dollars worth of sales each year. But in the US, PSK is little known, is not used by mainstream doctors, and until recently nothing like it was readily available. Now a nutritional supplement designed to be identical to PSK is available in the US, but very few mainstream doctors, and actually not many alternative practitioners are aware of it. So in the US, PSK has the status of a little known nutritional supplement or alternative therapy. Which is too bad in light of its proven benefits, easy administration, and lack of toxicity. Before I start sounding too much more like an advertisement, let me confess. I really am excited about it, but I have no financial interest in it; I'm not selling it.
Coriolus versicolor is a mushroom of the Basidiomycetes class. It was used initially in Traditional Chinese medicine as a tonic, but recent studies suggest that it has immunostimulant and anti-tumor properties. Polysaccharide-K (PSK), a proprietary product derived from Coriolus, was developed for cancer treatment in Japan. When used as an adjuvant, PSK appears to improve survival rates in patients with gastric (1) (2) and colorectal (3) (4) (5) cancers. Other Coriolus extracts, such as polysaccharide-peptide (PSP) and VPS, are available as dietary supplements. When used in conjunction with chemotherapy, PSP may benefit patients with advanced non-small cell lung cancer (7). Other clinical studies using Coriolus extract alone or in combination with other botanicals also suggest positive immunomodulatory effects (8) (9). However, studies on breast cancer (10), hepatocellular carcinoma (11), and leukemia (12) produced mixed results. A hot water extract of Coriolus, VPS, was found to enhance development of large intestinal tumors in mice (21). Coriolus extracts are generally well tolerated but minor adverse effects have been reported.
Many over-the-counter Coriolus products are not standardized, making it difficult to compare potency between brands. It is also unclear if PSK, PSP and other Coriolus extracts have comparable effects.
In 1994, I was introduced to PSK, and all-natural, high-quality extract product from the mushroom Coriolus versicolor. A neighbor introduced me to a local mycologist who enthusiastically told me about this remarkable product being used in Japan for the treatment of cancer.
Mushrooms have traditionally been valued in Asia for their nutritional and medicinal qualities. The Coriolus versicolor or "Turkey Tail" mushroom has been investigated in numerous laboratory, animal and human clinical studies. Most of these studies have demonstrated that it does appear to have significant antimicrobial, antiviral and antitumor properties when used as a supplement to chemotherapy and/or radiotherapy. Human trials have included randomization, a process that decreases bias, but only one has used blinding, which would make them even more protected against biases.