Turkey tail mushroom (Trametes versicolor) has been studied for its potential to support cancer patients undergoing chemotherapy, primarily due to its immunomodulatory properties. The most researched components are polysaccharide-K (PSK, also known as Krestin) and polysaccharide-peptide (PSP), both of which are isolated from turkey tail.

Clinical trials, mainly in Japan and China, have demonstrated that PSK, when used as an adjuvant with conventional chemotherapy, may enhance immune function and improve survival rates in patients with certain cancers, such as gastric, colorectal, and lung cancers. Some studies also report that patients taking PSK experience reduced chemotherapy-related side effects, such as fatigue, loss of appetite, and infection rates, likely due to improved immune response. For example, a meta-analysis published in 2012 in PLoS One reviewed randomized controlled trials and found a statistically significant improvement in 5-year survival rates in cancer patients using PSK as an adjunct to chemotherapy.

While not all formulations of turkey tail mushroom used in supplements have the same levels of PSK or PSP as those used in clinical trials, the existing evidence justifies its use as a supportive therapy. However, more large-scale, high-quality studies are needed to confirm efficacy and to standardize dosing. Overall, the current scientific evidence is promising, particularly for immune support and potentially mitigating some side effects of chemotherapy.