MALIGNANT-TUMOR OF THE RETINAL-PIGMENT EPITHELIUM WITH EXTRAOCULAR EXTENSION IN A PHTHISICAL EYE

Background: Malignant tumors of the retinal pigment epithelium (RPE) a re exceedingly rare. We describe the histopathologic and immunohistoch emical features of a RPE neoplasm that was found accidentally in a bli nd and painful phthisical eye. Methods: The enucleated eye was investi gated by light microscopy, and tumor tissue was also studied by electr on microscopy. Immunohistochemistry was performed using antibodies aga inst HMB-45, S-100 protein, NSE, cytokeratins, vimentin, desmin, GFAP, the HNK-1 carbohydrate epitope and alpha-smooth muscle actin. Results : The tumor was located mainly in the vitreous cavity with practically complete destruction of the retina, but foci of choroidal infiltratio n and extraocular extension along vascular channels were identified. T he mitotic rate was high, and large areas of necrosis were present. No features of differentiation were seen, apart from occasional desmosom e-like junctions and deposition of basal lamina at the ultrastructural level. Adjacent to the tumor, reactive hyperplasia and metaplasia of RPE cells was prominent. By immunohistochemistry, tumor cells revealed intense immunoreactivity with anti-vimentin and weak staining with an ti-S-100 protein. The hyperplastic RPE cells also reacted for cytokera tins 8, 18 and 19 and for alpha-smooth muscle actin. At more than 1 ye ar post enucleation the patient is well and shows no signs of recurren ce or metastatic disease. Conclusion: We present the features of a mal ignant tumor of the RPE with unequivocal extraocular extension. These findings raise the possibility that RPE hyperplasia may transform into a malignant tumor.