According to a literature search done in Medline and Cancerlit, no study has been published that shows that any of the mushroom therapies have efficacy as a cancer cure for humans. Both mushrooms produced very low TNF activity. The TNF capacity for production broadly parallels the survival rate of the mice transplanted with tumours. Suto and colleagues found no survival benefit to PSK in hepatocellular carcinoma patients after treatment with various standard therapies. There have been reports of toxicoderma, a skin disease.
Critics argue that prolonged and intense exposure to shiitake spores can be dangerous.
Workers exposed to high levels of such spores have been known to develop an occupational disease known as Mushroom Worker's Lung. However, the relevance of such findings to the ingestion of mushrooms is uncertain. It has been associated with severe dermatitis. One publication described 51 such complications. The shiitake mushroom contains agaritine, a hydrazine that has been shown carcinogenic in animals.