Primary cutaneous extraskeletal Ewing sarcoma of the scalp.

Primary cutaneous extraskeletal Ewing sarcoma (PCES) is an exceptionally rare variant of the Ewing sarcoma family of tumors, typically arising in the dermis or subcutis without osseous involvement. Due to its clinical mimicry of benign lesions and poorly defined dermoscopic features, early recognition can be challenging. To date, fewer than 20 well-documented cases have been reported in the literature. A 21-year-old male presented with a subcutaneous scalp mass with a reported 3-year clinical evolution. Dermatologic examination revealed a well-circumscribed vascularized lesion, and dermoscopy showed a polymorphous vascular pattern with arborizing and linear vessels, along with rainbow areas. Magnetic resonance imaging showed a non-invasive soft tissue mass. Histopathology confirmed a small round blue cell tumor with cluster of differentiation 99 (CD99) expression, and fluorescence in situ hybridization (FISH) analysis demonstrated Ewing sarcoma breakpoint region 1 (EWSR1) rearrangement, confirming PCES. The patient responded well to neoadjuvant chemotherapy and underwent surgical and radiotherapeutic management. This case is one of the very few reported instances of PCES with detailed dermatologic and dermoscopic documentation prior to oncologic intervention. It underscores the critical role of dermatologists in identifying rare soft tissue tumors. Prompt biopsy and molecular confirmation remain essential, and multidisciplinary care is key to improving outcomes in this rare malignancy.