[Myxoid variant of angiomatoid fibrous histiocytoma: a clinicopathologic analysis of 3 cases].

Objective: To study clinicopathologic features, diagnosis and differential diagnosis of myxoid variant of angiomatoid fibrous histiocytoma (AFH). Methods: Three cases of myxoid variant of AFHs were collected from First Affiliated Hospital of Nanjing Medical University during 2008 and 2017. EnVision method and fluorescence in situ hybridization(FISH) were used to detect immunophenotype and EWSR1 gene rearrangement, respectively. Results: There were 2 males and l female with age at 13, 31, and 42 years, respectively. The patients presented with a painless mass located superficially (subcutaneous or submucosal) in two cases or deep-seated (retroperitoneum) in one case. Grossly, the diameters of tumors were 1, 7, and 2 cm, respectively. The cut surface was solid and firm, tan to gray in colour. Histologically, the circumscribed tumor had fibrous pseudocapsule and peritumoal lymphoplasmacytic infiltrates. The tumor cells arranged in vaguely nodular growth pattern, with prominent myxoid stroma (present in 60% to 100% of the entire tumor). In hypocellular myxoid areas, the spindle to stellate tumor cells arranged in cords or reticular pattern, or in a haphazard manner. However, histiocytoid cells arranged in fascicular, sheet-like, or whorled growth pattern, as in classical AFH, were also identified in hypercelluar areas. Mild to moderate atypia was observed with low mitotic rate of (0-2)/10 HPF. Tumor necrosis was not seen. One case presented with slit-like hemorrhage and sclerosing collagen intermingled with myxoid matrix was identified in 1 case. Immunohistochemically, all cases were positive for CD68 and CD163. Two of three were positive for desmin, EMA, CD99 and one for Calponin, SMA. All cases were negative for S-100 protein, CD34, CD31, CD35, CD21 and CKpan. FISH detection was positive for EWSRl gene in all cases. Available clinical follow-up was obtained in 2 cases, revealing no evidence of disease in 6 and 89 months, respectively. Conclusions: Myxoid variant of AFH is a histological subtype of AFH, with clinical features, immunophenotypes, genomic profiles and biological behavior similar to typical AFH. Their unusual morphology is easily confused with a variety of other myxoid mesenchymal neoplasms, including myoepithelioma and nerve sheath tumors.