DEK::AFF2 Fusion-Associated Nonkeratinizing Squamous Cell Carcinoma with Noncontiguous Middle Ear and Sinonasal Involvement.

BACKGROUND

DEK::AFF2 fusion-associated nonkeratinizing squamous cell carcinoma is a recently recognized HPV-independent entity characterized by deceptively bland morphology and potential mimicry of benign or inflammatory lesions.

CASE PRESENTATION: A 21-year-old woman presented with recurrent left-sided otorrhea and progressive hearing loss. Imaging demonstrated noncontiguous lesions involving the left middle ear/mastoid compartment and the sinonasal region. Histologically, both lesions showed nonkeratinizing squamous proliferation with focal papillary/inverted architecture, mild to moderate cytologic atypia, and focal stromal invasion. Immunohistochemically, the tumor exhibited diffuse nuclear AFF2 expression, positivity for CK5/6 and p40, wild-type p53 expression, and negative p16 and INSM1. Targeted next-generation sequencing confirmed DEK::AFF2 fusion in both lesions.

CONCLUSION

This case expands the anatomic spectrum of DEK::AFF2 fusion-associated nonkeratinizing squamous cell carcinoma by demonstrating noncontiguous middle ear and sinonasal involvement. Recognition of its characteristic morphologic, immunophenotypic, and molecular features is essential to avoid misdiagnosis.