Solid Form of Angiomatoid Fibrous Histiocytoma: A Diagnostically Challenging Entity

Abstract

Aim: Angiomatoid fibrous histiocytoma (AFH) is a rare tumor mainly affecting children and young adults. The classic morphology is described as being well encapsulated with a solid cellular proliferation containing histiocyte-like cells, cystic/ hemorrhagic spaces and a surrounding dense lymphocytic infiltrate. Unfortunately, the morphology is not always typical and immunostains are often equivocal. Cytogenetic studies show that many instances of AFH have an EWSR1 gene rearrangement. We describe 8 cases of AFH and review them for lack of any of the characteristic histologic features. Methods and Results: Routine immunohistochemical (IHC) stains as well as FISH studies for EWSR gene rearrangement were preformed on available material. Seven of eight cases lacked at least one major histologic feature and three cases showed a uniformly solid architecture. In addition, three of the seven cases were positive for the EWSR1 gene rearrangement. Conclusion: It is important to recognize the solid form of AFH and not to confuse it with malignancy. FISH studies, when positive, are useful and practical in confirming the diagnosis of AFH in cases with unusual histology.