Turkey Tail Mushroom (PSK / PSP)

Trametes versicolor polysaccharides with the strongest survival data of any medicinal mushroom

Key Points

• Polysaccharide-K (PSK, krestin) and polysaccharopeptide (PSP) are protein-bound β-glucans from Trametes versicolor with immunomodulatory activity.
• PSK is an approved adjuvant cancer therapy in Japan, reimbursed under national insurance and used alongside chemotherapy for decades.
• The strongest data are in resected gastric and colorectal cancer: meta-analyses show improved 5-year survival when PSK is added to standard adjuvant chemotherapy.
• Acts primarily as a biological response modifier — restores T-cell and NK-cell function, increases dendritic-cell activity, and counteracts chemotherapy-induced immunosuppression.
• A US NIH-funded Phase I trial confirmed immune reconstitution (increased CD8+ T cells and NK activity) in breast cancer patients after chemoradiation.
• Excellent oral safety profile; the main practical caveat is product standardization — most US supplements are not standardized to PSK/PSP content.

Background and Active Constituents

Trametes versicolor (formerly Coriolus versicolor), commonly called turkey tail, is one of the most extensively studied medicinal mushrooms in oncology. Two protein-bound polysaccharide fractions carry the clinical evidence: **PSK (polysaccharide-K, marketed as krestin)** extracted from the CM-101 strain in Japan, and **PSP (polysaccharopeptide)** extracted from the COV-1 strain in China. Both are β-glucan–rich, protein-bound polysaccharides (roughly 25–38% protein) with molecular weights around 100 kDa. Unlike most botanicals in this reference, PSK is not a folk remedy — it is a…

Mechanism of Action

PSK/PSP act as **biological response modifiers** rather than direct cytotoxins. Their oncological effects are predominantly immune-mediated: - **T-cell restoration:** PSK counteracts chemotherapy- and tumor-induced immunosuppression, restoring CD4+/CD8+ T-cell numbers and function and normalizing the CD4:CD8 ratio. - **NK and dendritic cell activation:** PSK increases NK-cell cytotoxicity and promotes dendritic-cell maturation and antigen presentation. - **TLR signaling:** The β-glucan backbone engages Toll-like receptor 2 (TLR2) and dectin-1 on innate immune cells, driving cytokine…

Clinical Evidence

**Gastric Cancer:** A landmark meta-analysis (Oba et al., Cancer Immunol Immunother 2007) pooled 8 RCTs (n=8,009) of curatively resected gastric cancer and found that adding PSK to standard adjuvant chemotherapy significantly improved survival (odds ratio for death 0.88; 5-year survival benefit of ~9 percentage points in the highest-quality trials). **Colorectal Cancer:** A meta-analysis of RCTs in resected CRC (Sakamoto et al., Cancer Immunol Immunother 2006; 3 trials, n=1,094) demonstrated improved overall and disease-free survival when PSK was added to fluoropyrimidine-based adjuvant…

Clinical Applications and Dosing

**Adjuvant Immunosupport:** The best-supported use is as an adjunct to curative-intent surgery plus chemotherapy in gastric and colorectal cancer. In Japanese protocols, PSK 3 g/day orally (divided) is given alongside adjuvant chemotherapy and often continued for months to years. **Chemotherapy Tolerability:** In practice, integrative oncologists use turkey tail to help mitigate treatment-related immunosuppression and fatigue, based on the immune-reconstitution data. **Product Selection:** This is the key practical issue. Japanese and Chinese trials used pharmaceutical-grade PSK/PSP…