IMMUNOHISTOCHEMICAL EXPRESSION OF S-100-BETA IN CHOROIDAL MELANOMAS

Objective: To investigate the expressivity of S-100 beta antibodies in choroidal melanomas and to compare it with that of S-100 protein and HMB-45. Design: Twenty-seven choroidal melanoma specimens obtained fro m the McGill University Ophthalmic Pathology Registry were classified as spindle cell, epithelioid cell or mixed-cell type. Immunohistochemi stry was performed using the standard peroxidase-antiperoxidase techni que with monoclonal HMB-45, polyclonal S-100, polyclonal S-100 beta an d monoclonal S-100 alpha beta antibodies in formalin-fixed, paraffin-e mbedded sections. Outcome measure: Intensity of immunoreaction. The re sult was considered positive when at least five focal areas of stained cells were observed within the tumour. Results: All 27 tumours were p ositive for HMB-45, 19 (70%) for S-100, 23 (85%) for S-100 beta, and 2 1 (78%) for S-100 alpha beta. No correlation was found between the int ensity of the immunoreaction and cell classification, Conclusions: HMB -45 is the most reliable marker for choroidal melanomas, S-100 beta is a more sensitive marker than S-100 for choroidal melanomas regardless of cell type. Contrary to previous reports, S-100 beta should not be considered a useful immunomarker to differentiate between primary chor oidal melanoma and cutaneous melanoma metastatic to the choroid.