| Abstract: | Background: Angiomatoid fibrous histiocytoma (AFH) is typified by whirls of plump spindle cells with a triad of pseudoangiomatoid spaces, fibrous pseudocapsules, and lymphocytic cuffs. However, hallmark fusion genes in classical AFH are insufficiently characterized in variant cases. Design: Thirteen AFHs, including 11 with confirmed hallmark translocation, were reappraised for classic features, reactive osteoclasts, mitotic rates, and stromal, architectural, and cytomorphological variations, with CD99, desmin, and EMA stained in available cases. Results: Seven males and 6 females aged from 4 to 63 (median, 13) years, including 3 older than 30 years, had AFHs affecting the extremities (n=6), trunk (n=4), and scalp (n=3). Four showed solid histology devoid of pseudoangiomatoid spaces and another one lacked peripheral lymphoid infiltrates, while fibrous pseudocapsules were observed in each case. Nuclear pleomorphism was striking in 2 cases, moderate in 7, and absent in 4, with osteocalsts seen in 2 cases. In 3 AFHs with sclerotic stroma, one exhibited perivascular hyalinization and nuclear palisading, reminiscent of a schwannoma. In 3 varyingly myxoid tumors, one displayed prominent reticular arrangement of spindle cells in abundant myxoid stroma, resembling a myoepithelioma. Apart from split EWSR1 FISH signals in 4 cases tested, EWSR1-ATF1 fusion was detected in a myoepithelioma-like AFH and EWSR1-CREB1 in another 9, including a schwannoma-like case. Immunohistochemically, 56% of AFHs expressed EMA, 78% desmin, and 100% CD99. Conclusions: Molecular testing can aid in diagnosis of variant AFHs in an awareness of their diverse clinicopathological features. |
