Polysaccharide peptide (PSP) is a protein-bound polysaccharide extracted primarily from the mushroom Coriolus versicolor (also known as Trametes versicolor or "Turkey Tail"). Its use in supporting leukemia and other cancers stems from its immunomodulatory properties. Preclinical studies and some human clinical trials—primarily conducted in East Asia—have shown that PSP can stimulate immune responses, such as enhancing the activity of natural killer cells, T-cells, and macrophages. This has led to its investigation as an adjunctive therapy in cancer treatment, including leukemia.

In vitro and animal studies suggest that PSP may inhibit the proliferation of certain leukemia cell lines and induce apoptosis. A limited number of small clinical studies and case reports have explored the use of PSP in leukemia patients, mainly as an adjunct to chemotherapy, with some indicating improved immune parameters and quality of life. However, large-scale, high-quality randomized controlled trials in humans with leukemia are lacking, and the clinical benefit remains uncertain.

In summary, while there is a scientific rationale and some early evidence supporting the immunomodulatory and potential anti-leukemia effects of PSP, the evidence is not robust. Its use is not standard-of-care, and more research is needed to establish efficacy and safety in leukemia patients. PSP should not replace conventional leukemia treatments.