Adamantinoma-like Ewing's sarcoma with EWS-FLI1 fusion gene: a case report.

Recent studies have advocated the genotypic and phenotypic delineation of a novel Ewing's sarcoma histologic variant showing epithelial features defined as "adamantinoma-like Ewing's sarcoma". We described an 18-year-old girl with a primary small round-cell sarcoma of the right tibia showing polyphenotypic differentiation with epithelioid features. The neoplastic cells had mainly round or oval nuclei with fine chromatin with a portion of epithelial arrangements. The immunohistochemical analysis showed the epithelial markers of cytokeratin 5/6/18, AE1/AE3, and cytokeratin high molecular weight were stained especially in the foci with epithelioid features, as well as MIC2, S100, and NSE. The diagnosis of the lesion was confirmed as Ewing's sarcoma by the presence of the EWS-FLI1 fusion transcript, and could be defined as the so-called "adamantinoma-like Ewing's sarcoma". After wide excision and high-dose chemotherapy with peripheral blood stem cell transfusion, the patient has been well and continuously event-free for 3 years since the initial diagnosis.