Ultrastructural and immunomorphologic study of perinuclear filaments in Merkel cell tumors1

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Two cases of cutaneous small-cell tumor in patients without overt lung disease are presented. Histologic and ultrastructural findings support the diagnosis of Merkel cell tumor. Immunohistochemistry and immunoelectron microscopy demonstrate distinctive perinuclear keratin filaments that may be of histologic significance in separating a Merkel cell tumor from other nonendocrine tumors. A possible mechanism for the formation of perinuclear filamentous whorls is discussed.



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