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

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.