Grifola frondosa is a polypore mushroom that grows in clusters at the base of trees, particularly oaks. The fungus is native to the northeastern part of Japan and North America, and is prized in traditional Chinese and Japanese herbology as an adaptogen, an aid to balance out altered body systems to a normal level. Most Japanese people find its taste and texture enormously appealing, though the mushroom has been alleged to cause allergic reactions in rare cases. Cancer prevention is one of the purported uses of Maitake mushroom extract. Maitake is thought to exert its effects through its ability to activate various effector cells, such as macrophages, natural killer cells, T cells, interleukin-1 and superoxide anions, all of which have anti-cancer activity. In 2009, a phase I/II human trial showed Maitake could stimulate the immune system of breast cancer patients. Small experiments with human cancer patients revealed Maitake stimulated the patients' NK cells. In vitro research has also shown Maitake can stimulate the activity of NK cells. Experiments on cells have shown Maitake can induce apoptosis and inhibit metastasis. Apoptosis was induced in prostate cancer cells, and researchers have speculated the mushroom might be beneficial for people with this condition. In vitro experiments have revealed Maitake can inhibit the growth of various types of cancer cells. Small studies of human cancer patients revealed Maitake's in vitro anti-cancer activity may be relevant for people. An in vivo experiment showed that Maitake could stimulate the innate immune system and adaptive immune system of normal mice. Experiments have demonstrated Maitake can reduce blood sugar levels, and scientists speculate the mushroom may be beneficial for people with diabetes .