Endobronchial pulmonary angiomatoid fibrous histiocytoma: two cases with EWSR1-CREB1 and EWSR1-ATF1 fusions.

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue neoplasm of intermediate biological potential, predominantly occurring in the extremities of children and young adults. It has only recently been reported as a primary lung tumor. We describe 2 cases arising endobronchially harboring EWSR1 gene rearrangements by fluorescence in situ hybridization and, respectively, EWSR1-CREB1 and EWSR1-ATF1 gene fusions by reverse transcription polymerase chain reaction. Histologically, both tumors showed classical features of AFH, comprising multiple nodules of bland spindle to epithelioid cells surrounded by lymphoplasmacytic inflammation and at least a partial fibrous capsule. Both tumors showed focal but strong desmin immunoreactivity, with focal pancytokeratin and epithelial membrane antigen in 1 case. The lung is now a recognized site of AFH occurrence, but tumors arising here can be associated with different gene fusions. It is important to recognize AFH in the pulmonary region, as its behavior at other sites is generally relatively indolent; however, it may be mistaken for metastatic or more aggressive primary lung tumors. It is likely that cases of AFH in the lung may have been previously missed because of their morphologic and genetic overlap with other pulmonary lesions.