Numerous clinical trials have been carried out over the years with PSK derived from Trametes versicolor (Coriolus versicolor, Poyporous Versicolor, Turkey tail, Yun Zhi) and are briefly summarised below:

PSK:

There have been several decades of successful clinical trials using PSK to treat head and neck, upper GI, colo-rectal and lung cancers with some reported success in treating breast cancer as well.  Clinical trials with PSK have recently been extensively reviewed by Kidd (2000) and will be briefly summarised here.  Almost exclusively, clinical trials have been carried out in Japan.

PSK and gastric cancer:

PSK has been used as a form of immunotherapy for more gastric cancer patients than any other cancer type.  In early 1970s Kaibara’s group began trialing PSK with their existing chemotherapy regimens for stage IV disease (Kaibara et al., 1976).  After surgical resection (partial or full gastrectomies), PSK at 3g per day was added to a chemotherapy regimen of Mitomycin C and 5-fluorouracil (5-FU) (n=66). When compared with a historical control group, the 2 year survival rate was more than double, a finding that was later confirmed by Fujimoto et al. (1979) in a larger prospective study (n= 230).  Further studies by Hattori et al. (1979) (n=110) and Kodama et al. (1982) (n =450) suggested that PSK gave some protection against the immunosuppression that normally is associated with surgery and long-term chemotherapy.

One of the few double-blind randomised controlled trials (n=144) examining the role of single agent PSK found a significant increase in disease-free and overall survival.  PSK had significant effects on these patients immune systems as measured by increased delayed-type hypersensitivity on skin tests and enhanced chemotactic migration of neutrophils (Kondo and Torisu, 1985). All these studies suggest that individuals with very low immunity are less likely to benefit from PSK therapy than individuals with a reasonably competent immune system.  Other non- randomised trials in Japan have supported these findings (Mitomi and Ogoshi, 1986; Niimoto et al., 1988; Maehara et al., 1990; Nakazato et al., 1994).  Tsujitani et al. (1992) had previously observed that dendritic cells could infiltrate gastric cancers in some patients and biopsy examination correlated this dendritic infiltration of their tumours with an increase in disease-free and overall survival post-surgery.  It was concluded that patients with gastric cancer with limited dendritic cell infiltration prior to surgery when given PSK immunotherapy were more likely to have significant response.  The most recent phase III 2 arm trial of PSK in the treatment of gastric cancer carried out by the “Study Group of Immunochemotherapy with PSK for Gastric Cancer of Japan” showed that combining PSK with conventional chemotherapy significantly improved disease-free and overall survival (Nakazato et al., 1994).

PSK and other cancers

In a non-controlled, retrospective analysis of combined radiation, chemotherapy and immunotherapy (using PSK or OK-32, another immuno- potentiator) with 133 patients with oesophageal cancer, there were improvements in one-year and two-year survival (Okudaira et al., 1982).  In another more recent study PSK improved overall survival in oesophageal cancer in patients with levels of pre-operative high α1-anti-chymotrypsin or sialic acid (Ogoshi et al., 1995).  In a small scale trial in Taiwan for nasopharngeal carcinoma PSK adjunct therapy had a small but significant impact on five-year survival (Go and Chung, 1989).

In a study of 185 patients with epidermoid carcinoma, adenocarcinoma or large-cell carcinoma (≤ IIIb) given PSK as an immune system potentiator following radiotherapy, almost four times more patients who were treated with PSK had significant improvements in disease-free survival than those not given PSK (Hayakawa et al., 1993).  PSK was clinically significant with more advanced patients with Stage III disease than Stage I and II patients.  PSK had greater activity for older patients (> 70 years) and patients with small primary tumours. Early studies with breast cancer patients seemed to imply that long-term PSK immunotherapy in conjunction with chemotherapy could have beneficial results (Suginachi et al., 1984).  In a later much larger trial (914 patients) in-depth analysis implied that PSK significantly extended survival in ER-negative, Stage IIA patientswithout lymph node involvement (Toi et al., 1992).  However, in a further large trial, Morimoto et al. (1996) could find no statistical evidence of any benefit from PSK.

These contradictory studies may have been clarified by Yokoe et al. (1997) who compared HLA B40 antigen positive patients treated with PSK against B40 negatives.  It was found that B40-positive patients treated with PSK (3g/daily, two month course each year) in addition to chemotherapy had an improved 10 year overall survival rate compared to B-40 negative patients.  Thus, HLA B40 may be a predictive factor for PSK response.

The foregoing studies give strong indications of the potential benefits of incorporating PSK into some cancer treatments as an adjunct to radio- or chemotherapy.  Furthermore, PSK can improve immune status secondary to the side effects associated with traditional therapies.  As stated by Kidd (2000)  “after a quarter century of trials indicating PSK can improve cancer survival, the cumulative human findings amount to a recommendation for its inclusion in standard anticancer protocols. With its risk for adverse effects virtually nonexistent, PSK’s contribution to the benefit-risk profiles of these protocols can only be positive”.

Extracts taken from: THE ROLE OF POLYSACCHARIDES DERIVED FROM MEDICINAL MUSHROOMS IN CANCER (icnet.uk)