Schizophyllum commune, particularly its polysaccharide extract known as schizophyllan (SPG), has been investigated for its immunomodulatory properties and as an adjunct in cancer therapy. Several clinical studies, primarily from Japan, have evaluated schizophyllan in combination with chemotherapy for the treatment of various cancers, especially head and neck cancers and gastric cancer. The main rationale is that schizophyllan can enhance the immune response, potentially mitigating the immunosuppressive effects of chemotherapy and improving patient outcomes. Some studies have reported improved survival rates and quality of life when schizophyllan is used alongside conventional chemotherapy. There is also limited evidence that it may help reduce infection rates and some chemotherapy-induced side effects, such as leukopenia (low white blood cell counts).

However, while these findings are promising, most of the positive data come from small or regionally limited clinical trials, and systematic reviews have called for larger, high-quality studies to confirm efficacy and safety. Schizophyllan is approved as a biological response modifier in Japan, but is not widely adopted or licensed for this use outside of East Asia. The evidence supporting its use to reduce chemotherapy side effects is suggestive but not definitive, which is why it is rated as moderate (3/5) for evidence.