Benign clear cell (‘Sugar’) tumor of the lung A light microscopic, histochemical, and ultrastructural study with a review of the literature

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Abstract
A case of a benign clear cell “sugar” tumor of the lung is reported. Light microscopy showed a uniform proliferation of clear cells filled with abundant glycogen. At the ultrastructural level, tumor cells were rich in free monogranular and rosette-forming glycogen, but no membrane-bound glycogen was demonstrated. Some cells showed plasma membrane interdigitations, microvilli, and macula occludens-type junctions. Many polymorphic secretory and sporadic haloed neurosecretory-like granules were observed, but argyrophil stains as well as a large set of immunohistochemical reactions specific for APUD derivation had negative results. A literature review of this puzzling entity with particular emphasis on the histogenetic hypotheses is presented, and a derivation from epithelial nonciliated bronchiolar (Clara) cells or epithelial serous cells is suggested.