WT1 and Bcl2 expression in melanocytic lesions of the conjunctiva: an immunohistochemical study of 123 cases.

OBJECTIVE: Recent studies indicate that WT1 and Bcl2 protein are detected in melanocytic lesions of the skin. We examined, for the first time, WT1 and Bcl2 expression in a variety of conjunctival melanocytic lesions to evaluate their diagnostic utility compared with other melanocytic markers.

METHODS: Protein expression and localization of WT1 and Bcl2 were studied by means of immunolabeling and semiquantification in 123 conjunctival melanocytic lesions (71 benign nevi, 21 atypical nevi, 11 primary acquired melanosis, and 20 malignant melanomas). Ancillary immunohistochemical studies were performed with Bcl2, S100, HMB45, and Melan A antibodies.

RESULTS: WT1 showed a graded increase in expression in lesions with increasing atypia. Higher mean numbers of WT1-positive cells correlated with increasing atypia in melanocytes. In all cases, Bcl2 expression was positive and more robust than was S100, HMB45, or Melan A expression. WT1 and HMB45 frequently showed diffuse and strong staining in atypical nevi, primary acquired melanosis with atypia, and malignant melanomas compared with benign lesions.

CONCLUSIONS: Bcl2 is a highly sensitive immunohistochemical marker for melanocytic tumors of the conjunctiva; HMB45 and WT1 staining distinguishes benign from malignant lesions.

CLINICAL RELEVANCE: Our results show that HMB45 and WT1 immunolabeling is helpful in the evaluation of conjunctival melanocytic lesions. Accordingly, we recommend the development of an immunohistochemical panel to classify these lesions.