Background: HMB45 is a melanoma-associated antigen that is mainly expressed in immature melanocytes. It was also expressed in activated and neoplastic melanocytes and other neural crest-derived tumors. It was also expressed in normal breast epithelium, some normal sweat glands, sweat gland-derived tumors and angiomyolipoma, and occasionally in carcinoma. "It is more specific than S-100 or NKl/C3 for the diagnosis of malignant melanoma, but the sensitivity is less than 90%, especially in metastatic melanoma."