Comparison of immunohistochemical staining of the novel antibody melan-A with S100 protein and HMB-45 in malignant melanoma and melanoma variants.

AIMS: The staining pattern of the recently described antibody melan-A was compared with those of S100 protein and HMB-45 in a variety of melanocytic lesions to assess the specificity and sensitivity of these antibodies. METHODS AND
RESULTS: Immunohistochemical staining of paraffin sections of a range of melanocytic lesions was carried out following a high temperature antigen retrieval technique. The pattern and intensity of staining was semiquantitatively scored. S100 remains the most sensitive marker of melanocytic differentiation being diffusely positive in all benign and all primary and secondary malignant lesions including naevoid melanomas, and in most desmoplastic/spindle cell melanomas. Of the two more specific melanocytic markers melan-A stains the majority of benign and malignant lesions diffusely but with occasional patchy positivity only in some secondary melanoma deposits and with little staining of desmoplastic/spindle cell melanomas. HMB-45 is the least sensitive of the three showing little positivity of benign mature naevus cells, only variable patchy positivity of primary and secondary melanoma cells and limited positivity in naevoid, desmoplastic and metastatic melanomas.
CONCLUSIONS: Melan-A is a useful addition to antibody panels as it is apparently specific for melanocytic lesions and is more sensitive than HMB-45; however, it has less value than S100 in the detection of spindle cell and desmoplastic melanomas.