PAX8 Expression in the Crystalline Lens and Lens-Derived Lesions.

Purpose: To evaluate PAX8 expression by immunohistochemistry in the normal pediatric and adult crystalline lens and to assess the usefulness of PAX8 immunohistochemical stain in the diagnosis of morphologically challenging lesions of lenticular origin. Design: Retrospective, observational case series. Participants: Fourteen congenital and acquired lens-derived lesions and 10 control crystalline lenses. Methods: Hematoxylin-eosin and periodic acid-Schiff stains and an immunohistochemical panel of PAX8, vimentin, S100, smooth muscle actin, AE1/AE3, cytokeratin 7, and cytokeratin 5/6 antibodies were performed on all tissues. Main Outcome Measures: Distribution of PAX8 expression in normal crystalline lens and in lens-derived lesions. Results: Records search identified 10 normal pediatric and adult crystalline lenses, 1 phakomatous choristoma, 1 Peters anomaly with adherent leukoma, 1 lens capsule with congenital pyramidal cataract formation, 2 lenses with anterior and posterior subcapsular cataract formation, 3 postsurgical cataractous lenses (Soemmerring ring cataract and capsular fibrosis), and 6 retrocorneal membranes that incorporated various components of metaplastic corneal endothelium, metaplastic lens epithelium, corneal stroma, and epithelial downgrowth. Strong nuclear PAX8 expression was observed in the lens epithelium and in the equatorial lens bow of normal pediatric and adult lenses. Nuclear PAX8 expression also was observed in the lesions that retained some of the epithelial morphologic features, such as phakomatous choristoma, adherent leukoma, congenital pyramidal cataract, and components of intraocular membranes with lens epithelial differentiation. PAX8 expression was lost in lens epithelial lesions that had undergone mesenchymal transition, such as anterior subcapsular cataract and capsular fibrosis. Conclusions: PAX8 antibody may be a useful adjunct to the immunohistochemical panels in morphologically challenging lens epithelial-derived lesions that retain epithelial morphologic features. PAX8 is not useful in the diagnosis of lens-derived lesions that feature epithelial-mesenchymal transition.