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 Immunol Immunother. 2006;55(4):404–411.
Rationale
PSK (Krestin) — a protein-bound polysaccharide from Trametes versicolor — has been standard adjunctive therapy in Japanese colorectal-cancer care for decades. Individual trials suggested survival benefit; this meta-analysis pooled their individual patient data for a definitive estimate.
Methods
Individual-patient-data meta-analysis of 3 centrally randomized controlled trials: 1094 patients with colorectal cancer received PSK as an adjunct to standard chemotherapy after curative resection, with ≥5 years of follow-up.
Results
Pooled risk ratio for overall survival: 0.71 (95% CI 0.55–0.90; P=0.006). Disease-free survival: 0.72 (95% CI 0.58–0.90; P=0.003) — a consistent ~28–29% relative reduction in death and recurrence risk.
Conclusions
Adjuvant PSK after curative colorectal surgery produces a statistically robust improvement in both overall and disease-free survival — among the strongest quantitative results in mushroom oncology.
Worth noting
Individual-patient-data meta-analysis of centrally randomized trials is high-grade evidence. Context though: these are Japanese trials of a specific standardized preparation added to chemotherapy — not a claim for dietary turkey tail, and the regimen standards of the era differ from current practice. Still, for "does a mushroom preparation have a survival effect in cancer," this is as close to yes as the literature gets.