Case Report: SS18::POU5F1-fused sarcoma with Flexner-Wintersteiner rosettes: a clinicopathological analysis of a rare tumor in the submandibular gland.

SS18::POU5F1-fused sarcoma is an exceedingly rare malignant tumor, with only isolated case reports documented to date. We present the first reported case of SS18::POU5F1 fusion sarcoma occurring in the left submandibular gland of a middle-aged male patient. The tumor exhibited multiphasic differentiation, including epithelioid cells and undifferentiated round cell components, with focal evidence of neural differentiation and Flexner-Wintersteiner rosettes. It was characterized by the presence of a SS18::POU5F1 gene fusion. We provide a detailed description of the clinical features, histomorphology, immunophenotype, molecular characteristics, treatment, and prognosis of this case, discuss its differential diagnosis and potential pathogenesis, and include a comprehensive review of the relevant literature.