Edible mushrooms, such as reishi, maitake, and cordyceps, have long been used in Japan and China as food, but also medicines (Mizuno et al., 1995). These medicinal mushrooms have a deep history of medicinal use that extends back thousands of years in traditional Chinese medicine, and have long been associated with longevity (Castleman, 2001). In cancer research, there is special interest in the polysaccharides of these mushrooms present in the fruiting bodies and mycelium as they are responsible for anti-tumour and immunostimulating properties (Wasser, 2010). I will now critically discuss the current state of cancer science related to these polysaccharides and medicinal mushrooms.
A mushroom polysaccharide called polysaccharide-K (PSK) was originally extracted by Japanese researchers and used in various clinical trials in Asia together with conventional therapies (Fisher et al., 2002). The result of these trials were its acceptance as a mainstream anti-cancer drug in Japan to complement the existing chemotherapy and surgical techniques. PSK is a polysaccharide from the fungus Coriolus versicolor. PSK has shown efficiency in helping maintain remission in colorectal cancer patients after surgery (Torisu et al., 1990), a meta-analysis of different clinical trials in 2006 supported this discovery (Sakamoto et al., 2006). Another high quality study published in the Lancet found PSK supported ordinary chemotherapy treatment for gastric cancer after surgery and significantly increased five year survival and disease free survival rates (Nakazato et al., 1994). PSK increases the ability of the host to defend itself against the cancer (Fisher et al., 2002). It may do this by increasing white blood cell activation and response via increasing levels of specific cytokines. However, it is not just PSK which displays anti-tumour potential, there are several mushroom extracts which show promise.
A mushroom of particular value in traditional Chinese medicine is reishi, this mushroom has been known as ‘the mushroom of immortality’ since ancient times (Castleman, 2001). Reishi has an array of health benefits and has anti-oxidant, anti-tumour, anti-inflammatory properties (Joseph et al., 2011; Baskar et al., 2008). An interesting study appeared in the American journal PNAS in 2013 on the mechanism by which reishi has anti-tumour effects (Liao et al., 2013). In this paper, they demonstrated that mice injected with reishi polysaccharides produced antibodies against lung cancer cells. This resulted in increased cytotoxicity against the cancer cells and reduction of inflammatory mediators associated with the tumour. However, although promising, this study was using an animal model and high quality human clinical trials are required to further assess the anti-cancer potential of reishi.
There are a number of human studies with some preliminary data which is interesting. A randomised placebo controlled study of reishi polysaccharides in patients with lung cancer found increase in leukocyte and natural killer cell activity (Gao et al., 2003). They also observed better quality of life in the reishi mushroom patients and stability of disease. Improvements were seen in the reishi group in reduction of cancer related fever, cough, weakness, sweating and insomnia. The dose for this study was 600mg of patented extract a day, which seems a little low, as herbalists suggest between 3-6 grams of polysaccharide extracts for serious diseases like cancer (Powell, 2015). This translates to somewhere in the region of 10g of mycelium or fruiting body extract of reishi per day. However, this study only suggests that reishi may be effective as a complementary treatment for cancer patients, much further work is required (Gao et al., 2003).
Currently, we can be sure at least that reishi stimulates the immune system as this was seen in another well controlled human study also (Wicks et al., 2007). Another study documented a patient with breast cancer who used reishi extract as a complementary therapy (Chen et al., 2007). According to this account, reishi helped reduce side effects from chemotherapy and radiotherapy, improved quality of life, and assisted tumour shrinkage.
Like reishi, there is similar interest in the turkey tail mushroom (trametes versicolor) and a phase I clinical trial indicated immune up-regulation in breast cancer patients taking extract of this mushroom (Torkelson et al., 2012). This mushroom made headlines in 2012 as researchers were given $5.4 million for continuing their investigation of its ability to assist conventional cancer therapy. This is a very large amount of money for a complementary medicine study. These pioneering researchers of the turkey tail mushroom are aiming to create effective natural anti-tumour therapies without the harsh side effects of pharmaceutical drugs. Similar to reishi, the turkey tail mushroom has been shown to be effective against tumours in mice (Harhaji et al., 2008).
(Above) The maitake mushroom, another fungus where there is interest in it’s anti-tumour properties.
So it is not a good idea to throw away conventional medicine and run into the forest to hunt mushrooms. However, as research funding into complementary therapy grows, it is just a matter of time before convincing evidence regarding the human anti-tumor medicinal activity of mushrooms becomes available. In vivo and ex vivo experiments in experimental models imply mushrooms such as reishi, turkey tail, and cordyceps, will have a role in reducing side effects from chemotherapy, improving the efficiency of standard therapy, and possibly, even as a standalone therapy. The demonstrated efficiency of PSK in several high quality clinical trials supports the potential of medicinal mushrooms in the fight against cancer. What is needed now is more human clinical studies.
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Chen, Alice W., and John Seleen. “Potential benefits of Ling Zhi or Reishi mushroom Ganoderma lucidum (W. Curt.: Fr.) P. Karst.(Aphyllophoromycetideae) to breast cancer patients.” International Journal of Medicinal Mushrooms 9.1 (2007).
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