Angiomatoid fibrous histiocytoma: an expansion of the clinical and histological spectrum.

Angiomatoid fibrous histiocytoma, a fibrohistiocytic tumour of intermediate malignancy that usually presents on extremities of young patients, has a broader clinical/histological spectrum than is widely appreciated. We summarise our experience with an emphasis on unusual features. Twenty-seven cases were analysed for clinical and histological features, including immunohistochemistry and FISH for rearrangements of EWSR1 or FUS. Five (19%) occurred in patients >40 years old, and ten (37%) occurred outside the extremities. Three that occurred in patients >40 years old arose in atypical locations. Evaluation for classical histological features (lymphocytic cuff, fibrous pseudocapsule, pseudovascular spaces, haemorrhage, haemosiderin, and histiocytoid morphology) showed that all had two or more classical features. Unusual features were noted in many cases. Ten (37%) displayed significant areas of sclerosis; three of these ten had areas with a perineurioma-like pattern. Nine displayed at least moderate pleomorphism, with two exhibiting striking pleomorphism. Eight had eosinophils in the stroma, one with numerous eosinophils. One had a reticulated pattern of cells in a myxoid stroma. Mitotic rates were low [average 0.67/10 high power fields (HPFs)]. Three had atypical mitotic figures. Thirteen of 20 (65%) were CD68 positive, 11 of 17 (65%) were EMA positive, and 10 of 18 (56%) were desmin positive. Thirteen of 16 (81%) had a rearrangement of EWSR1; none had a FUS rearrangement.This series expands the spectrum of angiomatoid fibrous histiocytoma.