DEK::AFF2 rearranged neoplasm with undifferentiated morphology and neuroendocrine phenotype in a pediatric patient.

The advent of next-generation sequencing (NGS) has greatly enhanced the identification of morphologically and/or phenotypically unusual neoplasms. We report an undifferentiated carcinoma with a DEK::AFF2 fusion in a 13-year-old female from the head and neck region. DEK::AFF2 rearranged non-keratinizing squamous cell carcinoma (NKSCC) has been recognized as a distinct entity in the WHO classification of head and neck tumors, typically affecting adults. The case presented is unusual for both the patient's age and the undifferentiated morphology, which includes neuroendocrine immunophenotypic features, such as focal synaptophysin staining, dot-like cytokeratin expression, and only scattered cells positive for p63 and p40. Additional cases are needed to determine whether these features define a distinct subset of DEK::AFF2 rearranged neoplasms and to assess their potential correlation with a younger age of occurrence.