Hemangioblastoma-like clear cell stromal tumor of the lung.

The authors report 2 cases of an apparently unpublished stromal tumor of the lung characterized by a predominantly endobronchial growth pattern and benign-appearing clear cells. Both tumors were discovered incidentally in adult patients during routine workups for other medical reasons and treated with lobectomy. On gross inspection there was no evidence of infiltration of the adjacent lung tissue. Microscopically, both lesions featured monotonous oval-shaped to spindle-shaped cells growing in a vaguely nested pattern. The cytoplasm was slightly vacuolated or granular. In 1 case there was a variable admixture with mature fat. Immunohistochemistry was negative for markers of epithelial and stromal differentiation except for vimentin. A focal reaction for CD34 was seen in 1 case. No mutation of coding sequence of VHL gene was seen in one case. Medical follow-up at 1 year was negative for tumor recurrence or metastases. The broad differential diagnosis within the spectrum of stromal lung tumor is discussed. Owing to distinctive microscopic features such as the nesting of clear cells within a vascularized background, both tumors appeared similar to hemangioblastoma, although the expected immunohistochemical profile of the latter was not fully expressed. Because of pattern of growth seen in both lesions we believe that the appellation of endobronchial, hemangioblastoma-like clear cell stromal tumor may be provisionally designed.