Immunohistochemical studies of conjunctival nevi and melanomas.

OBJECTIVE To evaluate the role of immunohistochemical methods in the diagnosis of benign and malignant conjunctival melanocytic proliferations. DESIGN Retrospective immunohistopathologic study. METHODS Paraffin-embedded tissue sections from 20 conjunctival nevi and 15 invasive melanomas were immunoreacted with antibodies against cellular antigens S-100 protein, MART-1, HMB-45, CD-45, and Ki-67 nuclear proliferation protein. RESULTS All nevi immunostained moderately to strongly for S-100 protein and MART-1. Results for HMB-45 were negative in the middle and lower subepithelial portions of 18 of 20 lesions; it was usually only weakly positive within the superficial junctional zone. Only 1 melanoma did not stain positively for S-100; MART-1 and HMB-45 were positive in all lesions at some level of intensity. Ki-67 positivity was restricted to the junctional zone of nevi and was diffuse in melanomas. The mean Ki-67 proliferation indices were 1.89% for the nevi and 17.3% for the melanomas. CD-45 can help to highlight lymphocytes that immunostain with Ki-67. Melanomas in situ and atypical primary acquired melanoses had more than twice the Ki-67 proliferation counts of intraepithelial junctional nevocytes (P < .001) and more intense HMB-45 cytoplasmic staining than junctional zone nevocytes. CONCLUSIONS S-100 and MART-1 were not useful in separating benign from malignant lesions. Results for nevus cells beneath the junctional zone were overwhelmingly negative for HMB-45 and Ki-67. Two nevi and all melanomatous nodules were positive for HMB-45 (P < .001). A higher Ki-67 proliferation index convincingly separated melanomas from nevi (P < .001). Immunostaining for HMB-45 and Ki-67 are valuable adjuncts to careful histopathologic evaluation in assessing benign and malignant conjunctival melanocytic tumors.