This is a copper-containing oxidase that functions in the formation of pigments such as melanins and other polyphenolic compounds. Catalyzes the initial and rate limiting step in the cascade of reactions leading to melanin production from tyrosine. In addition to hydroxylating tyrosine to DOPA (3,4-dihydroxyphenylalanine), also catalyzes the oxidation of DOPA to DOPA-quinone, and possibly the oxidation of DHI (5,6-dihydroxyindole) to indole-5,6 quinone. Studies have shown tyrosinase to be a very specific marker for melanomas, not cross reacting with any other tumors or normal tissues tested Other studies have shown tyrosinase to be a more sensitive marker when compared to HMB-45 and MART-1. It has also shown to label a higher percentage of desmoplastic melanomas than HMB-45. However, both tyrosinase and MART-1 negative staining was seen in those variants without an epidermal component. Unlike HMB-45, neither tyrosinase or MART-1 discriminates between activated or resting melanocytes. In conclusion, tyrosinase appears to be a superior melanoma marker when compared to HMB-45.