Clear cell "sugar tumor" of the lung: Diagnostic features of a rare pulmonary tumor.

Clear cell tumor of the lung (CCTL) is an extremely rare neoplasm with about 50 cases reported in the literature so far. CCTL belongs to a family arising from putative perivascular epithelioid cells and is otherwise named as "sugar tumor" due to its high cellular glycogen concentration. Due to its rarity, diagnostic features of this entity are not widely known and this usually leads to misdiagnosis. Herein, we report a case of benign CCTL, which was primarily evaluated intraoperatively by FNA cytology and then by a pathological examination of the resected tumor. The cytologic preparations were moderately cellular and showed multiple large, irregular, cohesive clusters of ovoid or spindle tumor cells. Cells had clear cytoplasm, showing positivity with the periodic acid-Schiff (PAS) staining method owing to the glycogen (sugar) content. The rapid cytologic report excluded the possibility of malignancy and a middle lobectomy along with an anterior upper segmentectomy was performed. Immunochemistry revealed a diffuse positivity for HMB45, MART-1, SMA and focally for desmin, while specimen was negative for pancytokeratin cocktail AE1/AE3, cytokeratin7, cytokeratin20 and EMA. These findings confirmed the diagnosis of a benign CCTL. Due to its rarity and similarity with other clear cell tumors of the lung, awareness of this entity, recognition of the cytomorphologic features and familiarity with the associated clinical features can help clinicians avoid certain pitfalls in the diagnostic process. Considering its benign course, unnecessary extensive lung resections may also be avoided thus permitting conservative management of these patients.