Pseudomyogenic Hemangioendothelioma With Novel NEDD9::FOSB Fusion Gene

Pseudomyogenic hemangioendothelioma (PMHE) is a rare, low-grade vascular neoplasm that presents cutaneously as erythematous papules or nodules. Diagnosis is challenging, as PMHE can mimic more common benign dermatological conditions and shares histological similarities with high-grade tumors, particularly epithelioid sarcoma. We present the case of an 18-year-old male with a two-year history of a tender, indurated, dark brown subcutaneous plaque on his right upper thigh with histopathologic features consistent with PMHE. Genetic testing revealed a novel gene fusion, NEDD9::FOSB, which has not previously been reported in the literature, adding to the current genetic understanding of PMHE, and warrants further exploration as a potential therapeutic target.