Comparison of immunohistochemical labelling of melanocyte differentiation antibodies melan-A, tyrosinase and HMB 45 with NKIC3 and S100 protein in the evaluation of benign naevi and malignant melanoma.

A panel of three melanocyte differentiation antibodies has been compared with anti-S100 protein and NKIC3 in an assessment of benign and malignant melanocytic lesions. Anti-polyclonal S100 protein labelled all cases of primary cutaneous malignant melanoma, metastatic melanoma, desmoplastic melanoma and myxoid melanomas. In addition all benign and dysplastic naevi were positive. Conversely, HMB 45 was the least sensitive marker, labelling 24/31 primary cutaneous melanomas, 14/24 metastatic melanomas and only 1/6 desmoplastic melanomas. In the case of naevi, only junctional forms labelled consistently. Results for anti-melan-A and anti-tyrosinase were similar, although anti-tyrosinase proved slightly more sensitive in cases of malignant melanoma. NKIC3 revealed similar results to anti-tyrosinase, but had the disadvantage of reduced selectivity. It is concluded that anti-tyrosinase and anti-melan-A are useful additions to the panel of melanocytic monoclonal antibodies. In addition, both antibodies appear to have greater sensitivity for malignant melanoma than the conventionally used HMB 45 and could be considered as supportive markers to polyclonal anti-S100 protein in the diagnosis of malignant melanoma.