CLEAR-CELL TUMOR OF THE LUNG - AN IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY SUPPORTING A PERICYTIC DIFFERENTIATION

Clear cell tumor (''sugar tumor'') of the lung is a rare benign lesion with unclear histogenesis, It is composed of large cells with a clear cytoplasm rich in glycogen, blended with an abundant network of sinus oid-type vessels. We report two cases of sugar tumor, one of these lac king clearly demonstrable glycogen storage, In both, the tumor cells l acked keratin expression and were positive for vimentin and HMB 45, an antibody recognizing perivascular or myoid cell proliferation such as lymphangioleiomyomatosis and angiomyolipoma. The tumor cells were als o immunoreactive for an endothelial cell marker, CD 34, but negative f or Factor VIII or smooth muscle actin, Intercellular deposition of bas al-like material was immunostained with Type IV collagen. At ultrastru ctural examination of one of these cases, tumor cells showing features of pericytes or poorly differentiated perivascular leiomyocytes encas ed in basement material were observed in close association with endoth elial cells; their cytoplasm contained numerous membrane-bound glycoge n and pinocytic vesicles. We conclude that on the basis of immunohisto chemical and ultrastructural phenotype, sugar tumor presents pericytic features and that glycogen storage is not a constant feature of these benign tumors.