Protein-bound polysaccharide (PSK) has been used in traditional Chinese medicine (TCM) since the Ming Dynasty of China. In the 1980s, the Japanese government approved the use of PSK for treating several types of cancers. By 1984, it ranked 19th on the list of the world's most commercially successful drugs with annual sales of $255 million. PSK is obtained from cultured mycelia of the Coriolus versicolor , a mushroom thought to have antimicrobial, antiviral, and antitumor properties. PSK extracts are available for clinical use in Japan, where it is widely used for cancer immunochemotherapy. In Japan, PSK is currently used as a cancer treatment, in conjunction with surgery, chemotherapy, and/or radiation. Its active ingredient can be administered as a tea or in oral capsule form. In the United States, a similar product is labeled simply Coriolus versicolor extract. Coriolus versicolor is available in limited supply in U.S. markets. In Japan, PSK is currently the best-selling cancer medicine.