Abstract
Abstract: :
Purpose: Immunohistochemical detection of lens–specific differentiation protein expression in phakomatous choristoma (Zimmerman’s tumor), a rare benign tumor of lenticular anlage. Phakomatous choristoma (PC) is a lens tumor based upon its expression of crystallins and histological appearance, but its developmental origin as a lens epithelial cell or lens fiber cell tumor is not clear. The differentiation state of phakomatous choristoma can be assessed by examining PC for the expression of mature lens fiber cell–specific proteins. Methods: Immunohistochemistry with antibodies against lens–specific and non–specific proteins was performed to determine the protein expression profile of a 14 mm nasal left lower eyelid phakomatous choristoma surgically excised from a three month old boy. Results: Phakomatous choristoma prominently express MIP26, a lens fiber cell–specific membrane protein in the Wedl cells characteristic of PC. Filensin, a membrane– associated cytoskeletal protein expressed in lens fiber but not epithelial cells, was also expressed in the PC. This lens tumor also expressed alpha– and beta–crystallin, keratin, vimentin, S100, and collagen IV. The PC did not express cytokeratin, which is often expressed in lens epithelial cells. The PC also did not express calretinin. Conclusions: Phakomatous choristoma is a S–100 positive neuroectodermal lens tumor that expresses alpha, beta, and gamma lens crystallins. However, the differentiation state of PC cannot be concluded solely on lens crystallin protein expression. The expression of MIP26 and filensin, both lens fiber–specific proteins, demonstrates that PC has differentiated beyond the lens epithelium stage of development. PC is a benign lens tumor that is a mature lens fiber and not lens epithelium tumor.
Keywords: immunohistochemistry • oncology • orbit