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Pulmonary Pathology Online

Pathology of Clear Cell (Sugar) Tumour (PEComa) of the Lung

Dr Sampurna Roy MD





[" The benign clear cell tumor of the lung, also known as "sugar" tumor of the lung, is a very rare and somewhat controversial entity. The tumor was initially described by Liebow and Castleman in 1963  as "benign 'clear cell tumor'" of the lung. Subsequently, the same authors reported 12 examples of this tumor, using the modified term "benign clear cell ('sugar') tumor" of the lung. In a 1985 review, Andrion et al. had only identified an additional 10 tumors in the world literature.

The origin of "sugar" tumors of the lung has been debated. Although early studies suggested origin from smooth muscle or pericytes , neuroendocrine (Kulchitsky) cells , and epithelial nonciliated bronchiolar (Clara) or serous cells  , more recent studies have noted reactivity for HMB-45  and have shown ultrastructural evidence of melanocytic differentiation . Expanding on the latter concepts, Bonetti et al. proposed that clear cell tumors of the lung arise from the "perivascular epithelioid cell" or "PEC" and noted that similar cells have been identified in angiomyolipomas and lymphangiomyomas . In reporting a pancreatic sugar tumor, the same authors propose the term "PEComa" to describe these lesions."Modern Pathology - Primary Extrapulmonary Sugar Tumor ]

Clear-cell tumor of the lung is a rare entity of unknown etiology and histogenesis.

This neoplasm typically presents as an asymptomatic, peripheral, sharply rounded mass in the lung. 

Histologically, the tumour is composed of large polygonal tumour cells arranged in a diffuse growth pattern.

The cells have a clear cytoplasm, blended with an abundant network of sinusoid-type vessels.  

The clear cytoplasm contains numerous glycogen granules as demonstrated by PAS staining.

The tumor cells lack keratin expression and are positive for vimentin and HMB 45, an antibody recognizing perivascular or myoid cell proliferation such as lymphangioleiomyomatosis and angiomyolipoma .

The tumor cells are also immunoreactive for an endothelial cell marker, CD 34, but negative for Factor VIII or smooth muscle actin.  Strong immunostaining for type IV collagen is observed surrounding all the individual clear cells. 

Visit: Clear cell sarcoma and PEComas ; Clear Cell (Sugar) Tumour of the Pancreas.

Electron microscopically, clear cells have numerous membrane-bound glycogen granules and a large amount of non-membrane-bound glycogen.

The neoplastic cells are surrounded by external lamina and cytoplasmic processes.

The neoplastic clear cells show morphologic features seen in pericytes, melanocytic cells, and neuroendocrine cells.

Although most clear cell tumors are considered to belong to the family of neoplasms with perivascular epithelioid cell differentiation (PEComas), histogenesis of benign clear cell tumor of the lung has remained unclear.

Complete surgical excision is the treatment of choice.


Further reading:

Benign clear (sugar) cell tumor of the lung with CD1a expression.

Clear cell tumor of the lung.

The "sugar" clear cell tumor of the lung-clinical presentation and diagnostic difficulties of an unusual lung tumor in youth.

Clear cell tumor of the lung. A case report with review of the literature.

Clear cell tumor of the lung.

Clear cell tumor of the lung. Immunohistochemical and ultrastructural evidence of melanogenesis.

Clear cell tumor of the lung: an immunohistochemical and ultrastructural study supporting a pericytic differentiation. 

Clear-cell tumor of the lung: description of a case 1 mm in diameter ("micro-sugar tumor")

Benign clear cell tumor of the lung (sugar tumor). Morphologic, immunohistochemical and ultrastructural evaluation.

Benign clear cell tumor of the lung.

Sugar tumor of the lung--case report and review of the literature .

A rare cause of hemoptysis: benign sugar (clear) cell tumor of the lung.



Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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