Immunohistochemical studies of atypical conjunctival melanocytic nevi.

Objective: To evaluate with immunohistochemical methods 5 atypical melanocytic conjunctival lesions.

Methods: This was a retrospective clinicoimmunopathologic study. Routine histochemical staining was performed with multiparametric immunohistochemical analysis with monoclonal antibodies immunoreacted on paraffin sections to identify the following cell antigens: S-100, MART-1, HMB-45, CD45, CD68, CD1a, lysozyme, and Ki-67 (nuclear proliferation protein).

Results: A unique granular cell nevus contained periodic acid-Schiff-positive, diastase-resistant granules and immunoreacted with monoclonal antibodies against S-100 protein and melanocytic-associated antigens MART-1 and HMB-45. Results for CD45, CD1a, CD68, and lysozyme immunostaining of the granular cells were negative. Two epithelioid cell (clonal or inverted) nevi exhibited an identical immunohistochemical profile. Only the balloon cell nevus was MART-1-positive and HMB-45-negative. The granular cell and blue nevi immunoreacted negligibly with Ki-67 (approximately 1% of cells).

Conclusions: S100 and MART-1 reliably immunostained all nevocytic morphologic variants. HMB-45 immunoreactivity of the granular, epithelioid/clonal, and blue nevi did not indicate a more active or proliferative lesion but instead suggested abnormal melanogenesis. Ki-67 was the most valuable immunohistochemical adjunct to morphology for the diagnosis of these benign variant conjunctival nevi, because melanomas display a much higher proliferation index (>10% nuclear positivity among all cells counted) than the current nevi (approximately 1%).