Figure 1.

H&E stain findings of Ewing sarcoma. Most Ewing sarcomas demonstrate a classic histology with diffuse sheets of discohesive uniform small round cells (a). Primitive neuroectodermal tumor pattern features Homer Write rosettes, resembling neuroblastoma (b). Other uncommon patterns include reactive bone formation (c), prominent cytoplasmic clearing (d), and alveolar pattern (e). Large cell pattern is characterized by larger nuclear size and prominent nucleoli (f, a case with EWSR1::FLI1). Spindle cell pattern demonstrates swirling fascicles of short spindle cells, simulating synovial sarcoma (g, a case with EWSR1::FLI1). Nested epithelioid pattern is often confused with neuroendocrine tumors because of cohesive nests within the fibrous stroma (h, a case with EWSR1::FLI1). Adamantinoma‐like variant shows basaloid squamous differentiation with peripheral palisading and rare keratinization (i, a case with EWSR1::FLI1).