SINONASAL ADAMANTINOMA-LIKE EWING SARCOMA: A CASE EXPANDING THE MORPHOLOGIC SPECTRUM

Abstract

Adamantinoma-like Ewing sarcoma (ALES) is an exceedingly rare sinonasal malignancy defined by complex epithelial differentiation and EWSR1-FLI1 gene fusion. A 43-year-old female presented with painful facial swelling and proptosis. Computed tomography showed an exuberant heterogeneous tumor in the right sphenoid sinus that extended into the maxillary sinus, parapharyngeal space, orbit, and anterior cranial fossa. Microscopic analysis revealed sheets of monotonous basaloid cells with regular nuclear membranes and discernible nucleoli. Additionally, large foamy cells, ducts, whorls, and foci of abrupt keratinization were identified. Tumor cells were diffusely positive for AE1/3, p40, and CD99, and negative for NUT. The Ki-67 proliferation index was 40%. EWSR1 rearrangement was detected by FISH, confirming the final diagnosis of sinonasal ALES. Pathologists should consider ALES when evaluating aggressive sinonasal tumors composed of basaloid cells with focal keratinization. Immunopositivity for AE1/3, p40, and CD99, and molecular confirmation of EWSR1 rearrangement are essential for diagnosis. Adamantinoma-like Ewing sarcoma (ALES) is an exceedingly rare sinonasal malignancy defined by complex epithelial differentiation and EWSR1-FLI1 gene fusion. A 43-year-old female presented with painful facial swelling and proptosis. Computed tomography showed an exuberant heterogeneous tumor in the right sphenoid sinus that extended into the maxillary sinus, parapharyngeal space, orbit, and anterior cranial fossa. Microscopic analysis revealed sheets of monotonous basaloid cells with regular nuclear membranes and discernible nucleoli. Additionally, large foamy cells, ducts, whorls, and foci of abrupt keratinization were identified. Tumor cells were diffusely positive for AE1/3, p40, and CD99, and negative for NUT. The Ki-67 proliferation index was 40%. EWSR1 rearrangement was detected by FISH, confirming the final diagnosis of sinonasal ALES. Pathologists should consider ALES when evaluating aggressive sinonasal tumors composed of basaloid cells with focal keratinization. Immunopositivity for AE1/3, p40, and CD99, and molecular confirmation of EWSR1 rearrangement are essential for diagnosis.