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Case Reports

Abstract

Ewing sarcoma (ES) is typically a bone tumor of neuroectodermal origin primarily found in children. These tumors are very uncommon in patients over 40 years of age and rarely originate in extraosseous tissue. We present a 48-year-old man with a three-week-long perineal mass who underwent a skin biopsy. The biopsy showed epidermal ulceration and underlying dermis infiltrated with a small, blue cell tumor exhibiting prominent crush artifact. The cells stained positive for pankeratin and negative for CD20 and S100. The differential diagnoses was broad but the presence of such a small blue cell neoplasm at this location made metastatic small cell carcinoma from the lower gastrointestinal highly suspected. Next-generation sequencing (NGS) revealed an EWSR1-FLI1 chromosomal rearrangement, suggesting a diagnosis of metastatic or localized ES. CT scans showed no bone involvement, confirming the extra-osseous origin of tumor. ES is an extremely aggressive neoplasm and can metastasize to other sites, but despite its highly aggressive biological behavior, cutaneous metastases or primary ES of the skin are very uncommon. Even though the metastatic ES from the bone or primary cutaneous ES have been rarely reported, the extension from an extra-osseous tumor at older age has not been reported before. The rarity of this tumor in the skin and the unpredictable growth pattern of cutaneous metastasis, which may not reflect that of the primary tumor, pose diagnostic challenge. This case highlights the need to consider Ewing sarcoma in the differential diagnosis of cutaneous small blue cell neoplasms in patients of all ages.