Immunohistochemical evaluation of uveal melanocytic tumors. Expression of HMB-45, S-100 protein, and neuron-specific enolase.

The authors compared the immunohistochemical reactivity of 13 uveal nevi and 20 uveal melanomas for HMB-45, S-100 protein, and neuron-specific enolase (NSE) in formalin-fixed, paraffin-embedded sections. All 33 of the lesions were positive for HMB-45. The false-negative rates for S-100 protein and NSE were 21% and 18%, respectively. If only strongly positive reactions were considered, more than 50% of the tumors would be interpreted as negative for S-100 protein and NSE. Nevi stained with less intensity than melanomas using all three antibodies. The expression of HMB-45 appeared to be greater in active nevi than in inactive nevi. There was a weak association between S-100 protein reactivity and the ability of the uveal melanomas to metastasize (P = 0.1); however, the standard deviation of nucleolar area was a much better predictor (P = 0.02). These results indicate that pathologists will find HMB-45 to be a useful tool in differentiating uveal melanoma from nonmelanocytic tumors.