Aspiration biopsy cytology of benign clear cell ("sugar") tumor of the lung.

Benign clear cell tumor (BCCT) of the lung is an uncommon neoplasm, with about 24 cases reported in the literature. A fine needle aspirate from a histologically and ultrastructurally confirmed BCCT of the lung contained large irregular clusters of polygonal and spindle-shaped benign-appearing cells with vacuolated, granular, periodic-acid-Schiff-positive cytoplasm. Cytologic study of the aspirate suggested a pseudoinflammatory tumor; however, a metastatic renal cell tumor or a primary clear cell or mesenchymal tumor could not be excluded. The histologic, ultrastructural and cytochemical findings are also presented, and the cytologic differential diagnosis of this neoplasm is briefly discussed.