Rare FUS::FEV-Rearranged Adamantinoma-Like Ewing Sarcoma Arising in the Submandibular Gland.

BACKGROUND

Adamantimoma-Like Ewing Sarcoma (ALES) is a rare variant of Ewing sarcoma that poses significant diagnostic challenges in the head and neck due to morphologic overlap with basaloid carcinomas and neuroendocrine neoplasms.

CASE PRESENTATION: We report a case of a middle-aged man with a left submandibular gland mass showing classic histologic features of ALES, including basaloid nests with peripheral palisading, rosette formation, and high mitotic activity.

RESULTS

Immunohistochemistry showed co-expression of p63/p40, CD99, and cytokeratins, with patchy synaptophysin positivity and an elevated Ki-67 proliferation index. FISH for EWSR1 was negative, but next-generation sequencing identified a rare FUS::FEV fusion, previously reported only three times in ALES and never in the submandibular gland.

CONCLUSION

This case highlights the importance of extended molecular testing when EWSR1 FISH is negative; as alternate FET::ETS fusions may underlie the diagnosis.