Metastatic Malignant Pseudomyogenic Hemangioendothelioma: An Exceedingly Rare Entity That Challenges Conventional Paradigms

Pseudomyogenic hemangioendothelioma (PMHE), a rare soft tissue tumor predominantly affecting young adults, often presents as multiple nodules in various tissue planes of a limb. Malignant transformation and metastatic disease are unusual and pose diagnostic and therapeutic challenges. A 17-year-old patient from Western India, with a history of recurrent excisions for a toe swelling presented to our center for evaluation and management. A below-knee amputation was performed, and histopathology revealed PMHE. Adjuvant therapy was deemed unnecessary given the borderline nature of the tumor. Shortly thereafter, he developed features of local recurrence and underwent above-knee amputation. An expert histopathological review confirmed the diagnosis and noted features of malignant transformation–progression to a higher grade with greater cytological atypia, confluent growth, and increased mitotic activity over time. Upon further distant progression in the lung, he was started on a palliative regimen of weekly paclitaxel, vinblastine, and propranolol but eventually succumbed to his illness. In contrast to conventional descriptions of low mitotic activity, minimal nuclear atypia, and absence of necrosis, our patient exhibited increased mitotic rates, nuclear atypia, and evolving necrosis in serial histopathological evaluations. The fulminant clinical progression within a short interval was also atypical. Our patient's clinical course underscores the need for meticulous histopathological and molecular characterization and vigilant clinical surveillance after resection in patients with PMHE. Providing the standard of care for malignant disease in the adjuvant setting is challenging owing to the rarity and the lack of treatment guidelines.