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 from the McGill University Ophthalmic Pathology Registry were classified as spindle cell, epithelioid cell or mixed-cell type. Immunohistochemistry was performed using the standard peroxidase-antiperoxidase technique with monoclonal HMB-45, polyclonal S-100, polyclonal S-100 beta and monoclonal S-100 alpha beta antibodies in formalin-fixed, paraffin-embedded sections.

OUTCOME MEASURE

Intensity of immunoreaction. The result was considered positive when at least five focal areas of stained cells were observed within the tumour.

RESULTS

All 27 tumours were positive for HMB-45, 19 (70%) for S-100, 23 (85%) for S-100 beta, and 21 (78%) for S-100 alpha beta. No correlation was found between the intensity 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 choroidal melanoma and cutaneous melanoma metastatic to the choroid.