Test Details: Immunohistochemical testing is carried out on biopsy/resected tissue specimen. This testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody .HMB45 (human melanoma black 45) also known as gp100 is a melanosomal glycoprotein involved in the maturation of melanosomes from stage I to II. In normal tissue, HMB45 is found in retinal pigment epithelium and fetal melanocytes but absent in mature melanocytes and intradermal nevi. HMB45 is a marker for melanocytic tumours and tumours with melanocytic differentiation including different types of malignant melanoma, dysplastic nevi, Spitz and blue nevi, as well as clear cell sarcoma. About 10% of malignant melanoma (more frequently amelanotic melanoma, desmoplastic and spindle cell melanomas) lacks the HMB45 expression.