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.