Medicinal mushrooms have been used for hundreds of years, mainly in Asian countries, for treatment of infections. More recently, they have also been used in the treatment of pulmonary diseases and cancer. Medicinal mushrooms have been approved adjuncts to standard cancer treatments in Japan and China for more than 30 years and have an extensive clinical history of safe use as single agents or combined with radiation therapy or chemotherapy.
More than 100 species of medicinal mushrooms are used in Asia. Some of the more commonly used species include the following:
- Ganoderma lucidum (reishi).
- Trametes versicolor or Coriolus versicolor (turkey tail).
- Lentinus edodes (shiitake).
- Grifola frondosa (maitake).
Studies have examined the effects of mushrooms on immune response pathways and on direct antitumor mechanisms. The immune effects are mediated through the mushroom’s stimulation of innate immune cells, such as monocytes, natural killer cells, and dendritic cells. The activity is generally considered to be caused by the presence of high-molecular-weight polysaccharides (beta-glucans) in the mushrooms, although other constituents may also be involved. Clinical trials in cancer patients have demonstrated that G. lucidum products are generally well tolerated.
Several companies distribute medicinal mushrooms as dietary supplements. In the United States, dietary supplements are regulated as foods, not drugs. Therefore, premarket evaluation and approval of such supplements by the U.S. Food and Drug Administration (FDA) are not required unless specific disease prevention or treatment claims are made. Because dietary supplements are not formally reviewed for manufacturing consistency, ingredients may vary considerably from lot to lot and there is no guarantee that ingredients claimed on product labels are present (or are present in the specified amounts). The FDA has not approved the use of medicinal mushrooms as a treatment for cancer or any other medical condition.
Many of the medical and scientific terms used in this summary are hypertext linked (at first use in each section) to the NCI Dictionary of Cancer Terms, which is oriented toward nonexperts. When a linked term is clicked, a definition will appear in a separate window.
Reference citations in some PDQ cancer information summaries may include links to external websites that are operated by individuals or organizations for the purpose of marketing or advocating the use of specific treatments or products. These reference citations are included for informational purposes only. Their inclusion should not be viewed as an endorsement of the content of the websites, or of any treatment or product, by the PDQ Integrative, Alternative, and Complementary Therapies Editorial Board or the National Cancer Institute.
- Jin X, Ruiz Beguerie J, Sze DM, et al.: Ganoderma lucidum (Reishi mushroom) for cancer treatment. Cochrane Database Syst Rev 6: CD007731, 2012.
Turkey tail is a woody bracket polypore fungus that grows on dead logs worldwide. The scientific name of turkey tail is Trametes versicolor (L.) Lloyd, although it has been known by other names, notably Coriolus versicolor (L. ex Fr.) Quel. It is known as Yun Zhi in traditional Chinese medicine and Kawaratake (roof tile fungus) in Japan. The name turkey tail refers to its concentric rings of brown and tan, which resemble the tail feathers of a turkey. There are many other species of Trametes, some of which are difficult to distinguish from turkey tail. Internal transcribed spacer sequences alone have been found inadequate to distinguish turkey tail from other species of Trametes, so additional molecular characters are required for that task. Another Trametes species used primarily in China is Trametes robiniophila Murr, also known as Huaier.
The fungus has been used in traditional Chinese medicine for many years to treat pulmonary diseases.[2,3] A purified hot water extract prepared from the cultivated fungal mycelium has been used in Japan for its immunomodulatory effects as an adjuvant treatment for cancer.[4–6] Polysaccharide-K (PSK) or krestin, from the mushroom T. versicolor, is an approved mushroom product used for cancer treatment in Japan. PSK is a proprietary formulation from the Kureha Corporation. PSK has been used as an adjunctive cancer treatment in thousands of patients since the mid-1970s. The safety record for PSK is well established in Japan. Few adverse events have been reported in patients treated with PSK. Polysaccharopeptide (PSP) is another extract from T. versicolor produced in China.
The best known constituent of turkey tail is the glycoprotein mixture known as PSK. PSK is not a homogeneous substance, with a range of molecular weights averaging 9.4 kDa (range 5–300 kDa). The glycoprotein molecules are composed of a main chain beta-(1,4) glucan with beta-(1,3)– and beta-(1,6)–linked side chains. Small amounts of galactose, mannose, and arabinose have also been detected in the hydrolysate. Between 25% and 38% of the mass comes from a covalently linked protein whose amino acid composition has been reported.
PSK radiolabeled with carbon C-14 has been used to study the oral bioavailability and distribution of PSK in mice, rats, and rabbits. A fraction of the dose appears to be orally absorbed, more or less intact, and is excreted in bile over several hours. However, most of the radiolabeled dose is found in exhaled air, suggesting that the digestion of PSK may occur in the gut or the metabolism of absorbed PSK may occur somewhere else in the body. A monoclonal antibody (specific for PSK) that neutralizes PSK’s antitumor effects has been developed. It has been used to validate the presence of PSK in implanted tumors.
PSP, a very similar substance, has also been purified from a different strain of turkey tail; PSP and PSK differ somewhat in sugar composition.
A lipid component of PSK has been separated by lipase treatment and found to have toll-like receptor 2 agonist activity, synergistic with the protein-bound beta-glucan. The lipid component was primarily linoleic acid, with smaller amounts of other fatty acids.
Since the earliest reports of clinical benefits, other investigators have sought to define the mechanism of PSK’s beneficial action. One group hypothesized that T-cell dysfunction, including apoptosis of peripheral blood T cells, commonly occurs in patients receiving chemotherapy. They postulated that reversal of T-cell dysfunction induced by chemotherapy could reduce the adverse effects or enhance the antitumor effect. PSK is reported to enhance natural killer (NK) cell and T-cell activities by upregulation of interleukin-2 or interferon-gamma. Twenty patients with curatively resected stage III gastric cancer were randomly assigned to receive adjuvant therapy with the second-generation dihydropyrimidine dehydrogenase–inhibitory oral fluoropyrimidine S-1 alone (n = 10) or S-1 plus PSK (n = 10). At 5 weeks after adjuvant therapy, T-cell apoptosis was significantly higher in the S-1–alone group than in the S-1–plus-PSK group, leading the authors to conclude that PSK could partially prevent the T-cell apoptosis induced by S-1.
Another group of investigators studied the effect of PSK added to tegafur/uracil (UFT) chemotherapy compared with that of UFT alone. Baseline immune parameters were comparable in the two groups. However, CD57-positive T cells decreased more significantly after surgery for patients treated with PSK than for those in the control group (P = .0486). These investigators had previously noted that a high CD57-positive cell count was an indicator of poor prognosis in patients with advanced gastric cancer, leading them to suggest that PSK may improve overall survival (OS) partly by inhibiting CD57-positive T cells.
Noting that hosts become immunocompromised at the time of tumor progression and that decreased expression of major histocompatibility complex (MHC) class I by the tumor is one mechanism that allows it to evade destruction by cytotoxic T lymphocytes, investigators conducted a retrospective study to evaluate the expression of MHC class I by immunohistochemical staining in the primary lesions of patients with stage II or stage III gastric cancer. They analyzed data from 349 patients who had undergone adjuvant therapy (after curative resection) between 1995 and 2008; 225 patients received adjuvant chemotherapy with an oral fluoropyrimidine alone, while 124 patients received adjuvant chemotherapy plus PSK 3 g/d. Although this was not a randomized trial, baseline characteristics of the patients were well matched. The mean duration of follow-up was 49 months. Three-year recurrence-free survival (RFS) rates were the same for both groups (60% for the PSK group and 62% for the chemotherapy-only group). For MHC expression–negative cases, the 3-year RFS rates were 65% for the PSK group and 50% for the chemotherapy-only group; the difference was not considered significant. For 82 MHC expression–negative patients with lymph node status of pN2 or greater, the RFS rates were 65% for the PSK group and 34% for the chemotherapy-only group—a significant difference with no P value offered. The authors concluded that PSK adjuvant immunotherapy may be effective in MHC class I–negative patients with advanced lymph node metastasis of pN2 or greater.
While the mechanism of action for PSK in general and in colorectal cancer specifically is not clearly defined, the potential activity of PSK as an immunomodulatory adjunct to chemoradiation therapy in rectal cancer has been studied. Thirty patients with stage II or III rectal cancer who were treated with S-1 and external-beam radiation therapy were randomly assigned to receive either the standard regimen or standard regimen plus PSK. A number of cellular and humoral immune parameters were tested. An increase in peripheral blood NK cells after therapy was observed in the PSK-treated group compared with the control group. Immunosuppressive acidic protein (IAP) levels have been reported to be elevated in cancer patients and correlated to cancer progression and prognosis. In the study, a more-marked decrease in IAP level was observed in patients treated with PSK than in those treated in the control group. In addition, cytotoxic T cells increased in the peritumoral mucosa and normal mucosa within the radiation field in the PSK-treated group. The authors of the study concluded that PSK treatment may promote local tissue immunity within the radiation field.
One review included preclinical studies conducted in lung cancer models using either PSK or other T. versicolor preparations. Data from the 15 preclinical studies supported the anticancer effects of PSK by way of immunomodulation and potentiation of immune surveillance. In animal models, direct antitumor effects resulted in reduced tumor growth and metastases.
Gastric cancer is the most common malignancy diagnosed in Korea. Investigators in Korea performed a retrospective analysis of survival in patients who received PSK in addition to chemotherapy and in those who received chemotherapy only (control group). Unfortunately, the chemotherapy regimens differed in that the PSK patients were treated with fluorouracil and mitomycin-C (207 patients), while the controls received fluorouracil with doxorubicin-based chemotherapy (103 patients), introducing a potential bias in the interpretation of the results. Patients with all stages of gastric cancer were included in the analysis. Overall, there was no difference between groups in 5-year disease-free survival (DFS) or progression-free survival (PFS) rates. In a subgroup analysis, PSK recipients with stage IB or stage II disease showed superior 5-year survival (84.4% vs. 67.6%; P = .019), but no significant benefit was observed in patients with higher-stage disease.
Another retrospective analysis of nonrandomized data evaluated 254 patients with gastric carcinoma undergoing curative surgery with postoperative adjuvant treatment in Japan. Researchers compared 139 patients who received chemotherapy alone with 115 patients who received chemotherapy plus PSK. There were no significant differences between groups in patient demographics or tumor characteristics at baseline. There were no differences between groups in 5-year RFS rates (52.7% in the PSK group and 52.7% in the control group) or 5-year OS rates (57.1% in the PSK group and 58.3% in the control group). In a subset analysis of patients with more than seven involved lymph nodes (pN3), the 5-year OS rate was significantly higher in the PSK group (47.8%) than that in the control group (22.8%; P = .0317). Hence, these results contradict the findings from the Korean analysis.
A study published in 1994 first suggested the clinical benefit of adjuvant PSK for patients who underwent curative resection of gastric cancer in Japan. Investigators randomly assigned 262 patients who had undergone curative gastrectomy to receive either standard treatment with intravenous mitomycin and oral fluorouracil, or chemotherapy plus protein-bound PSK. Patients were monitored for 5 to 7 years. PSK improved both the 5-year DFS rate (70.7% vs. 59.4%; P = .047) and 5-year survival rate (73.0% vs. 60.0%; P = .044), compared with the standard treatment group. Treatment with PSK was well tolerated, with good compliance. The authors concluded that PSK should be added to standard chemotherapy for gastric cancer patients who undergo curative gastrectomy.
A 2007 meta-analysis included 8,009 patients from eight randomized controlled trials (RCTs) of adjuvant PSK in patients after curative resection of gastric cancers: 4,037 patients received PSK with chemotherapy, and 3,972 patients received the same chemotherapy alone. The OS hazard ratio was 0.88 (95% confidence interval [CI], 0.79–0.98; P = .018), indicating improved survival with the addition of PSK, with no significant heterogeneity between the treatment effects observed in the different studies. The three trials with the best quality supported the findings from the eight studies. The authors concluded that PSK was effective as adjuvant immunotherapy for patients with gastric cancer and suggested that this improvement may well be both statistically and clinically significant.
One other large study not included in this meta-analysis was a Japanese multicenter comparative trial of adjuvant chemotherapy versus adjuvant chemotherapy and PSK involving 751 patients undergoing curative resection, conducted from 1978 to 1981. Patients were randomly assigned to receive either chemotherapy with mitomycin-C plus oral tegafur (also known as futraful) with (n = 377) or without (n = 374) PSK 3 g/d. After reviewing 20 years of data, the investigators stratified patients on the basis of the ratio of their granulocytes to lymphocytes (G/L), believing that G/L ratios above 2.0 would predict responders. The 5-year OS rates were 67.9% in the PSK group and 61.8% in the control group (P = .053). In the subset of 364 patients with G/L ratios above 2.0, 5-year survival rates were 68.7% in the PSK group and 55.4% in the control group (P = .007). Because the G/L ratio was not related to stage, the authors suggested that the G/L ratio may be a host-dependent factor and might be useful to predict who might respond best to adjuvant PSK.
Finally, another small study has been reported since the meta-analysis. Patients received either oral UFT 300 mg/d or UFT plus PSK 3 g/d for at least 1 year after undergoing gastric resection for stage II or stage III gastric cancer. The 3-year survival rate was 62.2% in the 10 patients who received PSK and 12.5% in the 11 patients who received UFT alone (P = .038).
A U.S. National Institutes of Health-funded phase I clinical study that used a product containing T. versicolor mycelium grown on rice, which was then freeze-dried and heated, resulted in a statistically significant increase in CD8+ cytotoxic T cells (P = .0003), CD19+ B cells (P = .0334) and NK cells (P = .043) in a dose-dependent manner in breast cancer patients.
A retrospective study of the survival of 63 patients with colorectal cancer who were older than 70 years and treated with UFT with or without PSK included 24 patients who received UFT plus PSK. The 3-year relapse-free survival rates were 76.2% in the PSK group and 47.8% in the UFT-only group (control), and the 3-year OS rates were 80.8% in the PSK group and 52.8% in the control group.
One study analyzed outcomes from 101 patients at a single institution in Japan who had Dukes B or Dukes C colorectal cancer and were treated with UFT or UFT plus PSK for 24 months after curative surgery. These patients were monitored for up to 10 years after surgery. The 10-year survival was significantly better for patients treated with PSK, with a hazard ratio of 0.3.
Clinical studies of PSK in colorectal cancer have shown reduction in recurrence and improvement in OS with adjuvant use.
A meta-analysis of randomized, centrally assigned, prospective clinical trials of adjuvant therapy with PSK published between 1980 and 2004 identified three clinical trials that met selection criteria covering 1,094 patients. Combining the data from all three trials, the researchers found that the estimated odds ratio (OR) for the following:
- The 5-year DFS was 0.72 (95% CI, 0.58–0.90; P = .003, favoring PSK).
- The 5-year OS was 0.71 (95% CI, 0.55–0.90; P = .006, favoring PSK).
Thirty-one reports of 28 studies were included in a systematic review of PSK in lung cancer:
- Seventeen preclinical studies.
- Five nonrandomized controlled trials.
- Six RCTs.
All five nonrandomized controlled trials reported improved median survival with the use of PSK in combination with conventional radiation therapy and/or chemotherapy. PSK 3 g/d with concurrent chemotherapy was used in all RCTs, and all six studies showed benefit for at least one of the following endpoints:
|Reference||Trial Design||Product and Dose||Condition or Cancer Type||Treatment Groups (Enrolled; Treated; Placebo or No Treatment Control)b||Results||Concurrent Therapy Used||Level of Evidence Scorec|
|G/L = granulocyte to lymphocyte count; OR = odds ratio; PSK = polysaccharide-K; RCT = randomized controlled trial; UFT = tegafur/uracil.|
|aRefer to text and the NCI Dictionary of Cancer Terms for additional information and definition of terms.|
|bNumber of patients treated plus number of patient controls may not equal number of patients enrolled; number of patients enrolled equals number of patients initially recruited/considered by the researchers who conducted a study; number of patients treated equals number of enrolled patients who were given the treatment being studied AND for whom results were reported.|
|cStrongest evidence reported that the treatment under study has activity or otherwise improves the well-being of cancer patients. For information about levels of evidence analysis and an explanation of the level of evidence scores, refer to Levels of Evidence for Human Studies of Integrative, Alternative, and Complementary Therapies.|
|||RCT||PSK (3 g/d)||Gastric cancer||751; 376; 374 (groups were stratified by G/L ratio of <2 vs. >2)||Overall 5-y survival: all patients, 67.9% (PSK) versus 61.8% (control) (P = .053); for G/L ratio ≥2: 68.7% (PSK) versus 55.4% (control) (P = .007)||Mitomycin-C plus tegafur||1iDii|
|||RCT||PSK (3 g/d)||Gastric cancer||262; 124; 129||Improved survival in the treatment group was clinically significant||Mitomycin-C plus oral fluorouracil||1iDiii|
|||RCT||PSK (3 g/d)||Gastric cancer||21; 10; 11||Survival was improved significantly in treatment group||UFT 300 mg/d starting 2 wk after surgery and continuing for 1 y or until diagnosis of tumor recurrence||1iDii|
|||Meta-analysis summarizing 48 studies||PSK (various doses)||Colorectal cancer||3 trials; 1,094 patients||5-y survival: 79.0% (chemotherapy plus PSK) versus 72.2% (chemotherapy alone) (OR, 0.71; P = .006)||Mitomycin-C plus long-term administration of oral fluorinated pyrimidines||1iB|
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