Turkey Tail / PSK

The strongest clinical evidence here belongs to PSK (polysaccharide-K, Krestin), a defined preparation. It does not transfer automatically to generic Turkey Tail powders, capsules, teas, tinctures or supplements.

Proposition / claim

Historical adjunctive benefit from PSK in specified postoperative gastric and colorectal cancer treatment settings.

Evidence owner

PSK / Krestin — the defined Trametes versicolor-derived preparation investigated in the historical adjunctive oncology programmes. The biological source is Trametes versicolor; the clinical evidence owner is PSK. PSK evidence is not generic Turkey Tail evidence.

Dominant uncertainty

Contemporary incremental clinical benefit. The dominant uncertainty is contemporary clinical transportability. Historical randomized PSK programmes tested the intervention alongside the standards of care of their era. Surgery, staging, chemotherapy, targeted therapy, immunotherapy, supportive care and surveillance have since changed substantially. The historical results remain evidence within their original context, but they do not establish what incremental benefit PSK would provide alongside contemporary oncology. The control arm moved.

Organism

Trametes versicolor

Tested intervention

PSK / polysaccharide-K / Krestin

Evidence target

Standardized preparation

Intervention description

Defined protein-bound polysaccharide preparation historically produced from cultured mycelial material of Trametes versicolor (Coriolus versicolor), including the clinically documented CM-101 lineage.

Population

Patients in the specified historical postoperative gastric and colorectal cancer treatment programmes represented by the audited PSK evidence.

Comparator

Historical conventional treatment / chemotherapy without adjunctive PSK.

Outcome

Clinically important survival outcomes, including disease-free survival and overall survival in the specified historical oncology programmes.

Evidence maturity (E)

E4-H+

Direction

+ — Supports the tested proposition

Historical flag (H)

H — historical evidence flag present in the source grade

Replication (R)

R4

Claim Gap (CG)

Claim ceiling: CG1 for PSK-specific historical wording. CG0 — Historical randomized oncology trials found adjunctive benefit from PSK in defined gastric and colorectal treatment settings. CG1 — PSK has substantial historical adjunctive cancer evidence. CG1–2 — A Turkey Tail-derived medicine has shown clinical benefit in some cancers. CG3 — Turkey Tail helps cancer treatment. CG4 — Turkey Tail fights cancer. CG4 — Turkey Tail supplements are clinically proven to fight cancer. The ladder exposes Preparation / Intervention Identity Collapse.

Evidence Transfer Vector

Transferred proposition: "Turkey Tail supplements improve survival during modern cancer treatment." ETV: I / C / D / R. I — Intervention: PSK → generic Turkey Tail supplement. C — Clinical context: historical oncology regimens → contemporary oncology. D — Dose/route: the defined historical clinical exposure → unspecified commercial-product exposure. R — Replication/certainty: historical PSK programme → assumed modern product/setting efficacy.

Taxonomic Transfer Confidence

Historical Coriolus versicolor → modern Trametes versicolor: HIGH. Taxonomic continuity is not intervention equivalence: high TTC does not imply high transfer confidence from PSK to Turkey Tail supplements.

Intervention Transfer Confidence

PSK → arbitrary Turkey Tail supplement: LOW. "Derived from" does not mean "equivalent to."

Safety

S2, with combination-treatment qualification

Conservation

C0

Resolution zone

RZ-3 — large contemporary confirmatory programme

Next best experiment

A contemporary randomized add-on trial of standardized PSK against current standard-of-care oncology in a carefully chosen indication. The primary endpoint should be clinically meaningful — for example disease-free survival, progression-free survival or overall survival where appropriate — rather than an easily moved surrogate biomarker.

Primary references

1. 1.Nakazato H, Koike A, Saji S, Ogawa N, Sakamoto J; Study Group of Immunochemotherapy with PSK for Gastric Cancer. Efficacy of immunochemotherapy as adjuvant treatment after curative resection of gastric cancer. Lancet. 1994;343(8906):1122–1126. PMID: 7910230. DOI: 10.1016/S0140-6736(94)90233-X. — Primary randomized gastric-cancer evidence. Multicentre study conducted at 46 institutions in Japan involving 262 patients after curative gastrectomy. PSK was tested as an adjunct to the conventional chemotherapy regimen used in that historical treatment setting, not as a stand-alone cancer treatment and not as ordinary Turkey Tail. Five-year disease-free survival was 70.7% with PSK-containing treatment versus 59.4% with standard treatment; five-year survival was 73.0% versus 60.0%. This reference supports the historical PSK-specific positive clinical signal while remaining subject to the dossier's Historical flag and contemporary-transport limitation.
2. 2.Sakamoto J, Morita S, Oba K, Matsui T, Kobayashi M, Nakazato H, Ohashi Y; Meta-Analysis Group of the Japanese Society for Cancer of the Colon Rectum. Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curatively resected colorectal cancer: a meta-analysis of centrally randomized controlled clinical trials. Cancer Immunology, Immunotherapy. 2006;55(4):404–411. PMID: 16133112. DOI: 10.1007/s00262-005-0054-1. — Principal colorectal PSK synthesis. Meta-analysis of 1,094 patients from three centrally randomized clinical trials following curative colorectal-cancer resection. Standard chemotherapy was compared with chemotherapy plus PSK. The pooled analysis favoured PSK-containing treatment for overall survival and disease-free survival. This is evidence concerning adjunctive PSK within the historical programmes represented by the included trials. It does not establish equivalence between PSK and arbitrary Trametes versicolor products and does not establish contemporary incremental benefit alongside present-day oncology.
3. 3.Ohwada S, Ikeya T, Yokomori T, Kusaba T, Roppongi T, Takahashi T, Nakamura S, Kakinuma S, Iwazaki S, Ishikawa H, Kawate S, Nakajima T, Morishita Y. Adjuvant immunochemotherapy with oral Tegafur/Uracil plus PSK in patients with stage II or III colorectal cancer: a randomised controlled study. British Journal of Cancer. 2004;90(5):1003–1010. PMID: 14997197. PMCID: PMC2409633. DOI: 10.1038/sj.bjc.6601619. — Randomized colorectal PSK evidence contributing to the historical clinical programme. The analysed cohort contained 205 patients. Five-year disease-free survival favoured the PSK-containing arm (73.0% versus 58.8%). Whole-cohort five-year overall survival was 81.8% versus 72.1%, with P=0.056. Preserve the distinction between the disease-free-survival result and the less conclusive whole-cohort overall-survival result. Do not convert this study into a generalized claim that Turkey Tail improves cancer survival. Bibliographic metadata independently verified against PubMed and Crossref records rather than reconstructed.
4. 4.Pilkington K, Wieland LS, Teng L, Jin XY, Storey D, Liu JP. Coriolus (Trametes) versicolor mushroom to reduce adverse effects from chemotherapy or radiotherapy in people with colorectal cancer. Cochrane Database of Systematic Reviews. 2022;11:CD012053. PMID: 36445793. PMCID: PMC9707730. DOI: 10.1002/14651858.CD012053.pub2. — Principal modern certainty/transportability reference. Cochrane included seven randomized controlled trials involving 1,569 participants. All seven studies used Coriolus/Trametes extracts rather than ordinary dietary Turkey Tail. The review found low-certainty evidence of a small improvement in five-year survival and very-low-certainty evidence for many adverse-effect outcomes. It also noted that chemotherapy regimens contributing to the survival evidence do not reflect current preferred practice. This reference is essential to the dossier because it preserves the distinction between a historical positive signal and confidence in contemporary transportability. It must not be represented as showing that ordinary Turkey Tail supplements treat cancer.

Source chapter

Chapter 10, The Fungal Evidence Atlas