Myxoid and reticular angiomatoid fibrous histiocytoma: a case confirmed by fluorescence in situ hybridization analysis for EWSR1 rearrangement

Angiomatoid fibrous histiocytoma (AFH) is a tumor of intermediate malignancy and undefined lineage, mostly arising in the extremities of young patients. However, AFH may rarely display uncommon clinical and morphologic features, such as older age at presentation, occurrence outside somatic soft tissues and alterations in the architectural patterns, stromal matrix and cytomorphology, causinga great diagnostic challenge for practicing pathologists. Herein, we present a case of AFH with unusual histologic features arising in the right hip of a 37-year-old man. The tumor exhibited a reticular growth pattern and myxoid stroma mimicking myoepithelioma, extraskeletal myxoid chondrosarcoma, or myxoid liposarcoma. The tumor cells focally expressed desmin with a dendritic-like cell process staining pattern and CD68. Fluorescence in situ hybridization analysis confirmed the rearrangement of the EWSR1 gene. This report further expands the clinicopathologic spectrum of AFH and underscores the value of integrating morphologic, immunophenotypic, and molecular findings in the identification of its unusual morphologic variants.