Evaluation of melanocytic neoplasms: application of a pan-melanoma antibody cocktail

Incidence of malignant melanoma (MM) is rising rapidly throughout the Western world, and the number of melanocytic lesions removed for histological assessment has increased. MM can present with a myriad of histological appearances that make diagnosis problematic, particularly when dealing with metastatic deposits. Immunohistochemical diagnosis relies on a panel of antibodies comprising polyclonal S100 protein and the monoclonal antibodies HMB 45, MART-1, tyrosinase and, to a lesser extent, NKIC3. Confirmation of problematic cases relies on the use of polyclonal S100 protein, as its sensitivity has yet to be matched by any monoclonal antibody. The introduction of a potentially valuable pan-melanoma cocktail, composed of HMB 45, MART-1 and tyrosinase, is examined in 50 primary cutaneous malignant melanomas, five desmoplastic malignant melanomas (DMM), 35 benign naevi, 20 metastatic malignant melanomas, 10 basal cell carcinomas (BCC) and 10 squamous cell carcinomas (SCC) and compared to individual immunolabelling with S100 protein, HMB 45, MART-1 and tyrosinase. All BCCs and SCCs were negative with all antibodies. S100 protein, MART-1, tyrosinase and the pan-melanoma cocktail were positive for all cases of benign naevi. HMB 45 labelled all junctional and compound naevi, five of the eight intradermal naevi and five of the seven blue naevi. All 50 primary cutaneous MMs were positive with S100 protein, 49/50 with the pan-melanoma cocktail and tyrosinase, 47/50 with MART-1 and 46/50 with HMB 45. Of the five cases of DMM, all were positive with S100 protein and three of the five were positive with HMB 45, MART-1, tyrosinase and the pan-melanoma cocktail. In the case of metastatic MM, all 20 cases were positive with S100 protein, the pan-melanoma cocktail and tyrosinase. MART-1 was positive in 19/20 cases and HMB 45 in 17/20 cases. The pan-melanoma cocktail showed a high sensitivity for all forms of MM and should be considered a complementary marker to polyclonal S100 protein. Results confirmed that currently there is no alternative antibody available to match the sensitivity of polyclonal S100 protein for immunolabelling DMM.