A rare case of primary vulvar Ewing sarcoma: Diagnostic and therapeutic challenges in an unusual presentation

The Ewing sarcoma family includes various bone and soft tissue tumors showing different degrees of neuroectodermal characteristics. Ewing's sarcoma primarily impacts the bones, with occurrences outside of these structures being quite rare. Extraosseous Ewing's sarcoma (EES), found outside of bones, is exceptionally rare, posing distinct diagnostic and therapeutic challenges. We describe a 49-year-old patient diagnosed with Ewing's sarcoma of the vulva. The patient initially noticed a painful vulvar mass measuring 3 cm in diameter near the urinary meatus. Imaging revealed a 5 cm tumor on the bladder's posterior base, extending into the pelvic fat. Initially misdiagnosed as a poorly differentiated infiltrating carcinoma, subsequent immunohistochemical staining identified the mass as vulvar Ewing sarcoma/PNET, with cells showing focal PS100 positivity and CD99 membrane positivity. A pelvic MRI confirmed 6.7 × 3.4 cm mass invading vulvar tissue. Further imaging and a bone marrow biopsy excluded metastasis. The treatment regimen included seven rounds of intensive chemotherapy using the VAC/IE protocol, supplemented by local definitive radiotherapy after the third chemotherapy cycle, showing positive results. The treatment plan was to continue with adjuvant chemotherapy. After four months, no disease recurrence was observed. This report details an uncommon case of EES that developed in the vulva, exploring its clinical signs, diagnosis, and treatment methods.