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 mel anocytic lesions to assess the specificity and sensitivity of these an tibodies. Methods and results: Immunohistochemical staining of paraffi n sections of a range of melanocytic lesions was carried out following a high temperature antigen retrieval technique, The pattern and inten sity of staining was semiquantitatively scored, S100 remains the most sensitive marker of melanocytic differentiation being diffusely positi ve in all benign and all primary and secondary malignant lesions inclu ding naevoid melanomas, and in most desmoplastic/spindle cell melanoma s, Of the two more specific melanocytic markers melan-A stains the maj ority of benign and malignant lesions diffusely but with occasional pa tchy positivity only in some secondary melanoma deposits and with litt le staining of desmoplastic/spindle cell melanomas, HMB-45 is the leas t sensitive of the three showing little positivity of benign mature na evus cells, only variable patchy positivity of primary and secondary m elanoma cells and limited positivity in naevoid, desmoplastic and meta static melanomas. Conclusions: Melan-A is a useful addition to antibod y panels as it is apparently specific for melanocytic lesions and is m ore sensitive than HMB-45; however, it has less value than S100 in the detection of spindle cell and desmoplastic melanomas.