Adamantinoma-like Ewing family tumor of soft tissue associated with the vagus nerve: a case report and review of the literature.

Adamantinoma-like Ewing family tumor (EFT) is a rare subset of EFTs showing mixed features of Ewing sarcoma and adamantinoma of the long bones. All currently reported cases of the adamantinoma-like type have been associated with bone. Recently, a unique type of EFT was reported showing complex epithelial differentiation associated with the vagus nerve. Here we describe another unique type of EFT arising in the soft tissue of the neck associated with the vagus nerve. An 11-year-old girl presented to our hospital with a neck tumor on her right side. Surgical resection was performed, and histopathologic examination demonstrated a high-grade malignant neoplasm. The tumor was composed of sheets of small round proliferating cells, basaloid tumor nests with marked squamous differentiation, biphasic growth pattern with epithelioid tumor nests, and spindle cell proliferation. Immunohistochemically, the tumor cells showed diffuse expression of CD99 and FLI-1. In addition, small round cells and basaloid/squamoid components were immunoreactive for AE1/AE3, CAM5.2, cytokeratin 5/6, high-molecular weight keratin, p63, and p40 (ΔNp63). Reverse transcription polymerase chain reaction and direct sequencing analysis revealed that the tumor harbored a t(11;22) translocation, involving EWSR1 and FLI-1, which are characteristic of EFTs. According to these findings, our case has characteristics of both a subset of adamantinoma-like EFT and EFT with complex epithelial differentiation. We suggest that EFT with complex epithelial differentiation is in a common spectrum with the adamantinoma-like type and that adamantinoma-like EFTs can arise in soft tissue, leading to difficulty in differential diagnosis with malignant epithelial tumors.