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Case of the Month: June 2023

posted: June 29, 2023

This is a 73-year-old female with right knee pain for few months. MRI was performed and shows a 7.5 cm a heterogenous soft tissue lesion. A biopsy is taken.

View Final Diagnosis
Final Diagnosis: Epithelioid Hemangioendothelioma (EHE)
Epithelioid hemangioendothelioma (EHE) is a rare, low-grade malignant vascular neoplasm that primarily affects adults (rare in children) and carries a metastatic potential. The pathogenesis of this tumor is not well understood, and risk factors have not been identified. It can occur in multiple parts of the body such as lung, soft tissue, head & neck, pleura, bones and many other organs, as a single or multifocal lesions. The term epithelioid hemangioendothelioma was introduced in 1982 by Weiss and Enzinger to describe a vascular tumor of bone and soft tissue showing features between hemangioma and angiosarcoma.
Usually, the tumor grows as a well-defined nodule which can be single or multiple with variable sizes. The tumor appears in nests or cords of epithelioid or dendritic-looking cells that spreads through a myxoid or hyalinized stroma and infiltrates the surrounding soft tissue. Some cells show intracytoplasmic lumina. The Tumor cells express vascular markers, such as CD31, ERG, and FLI1. Cytokeratin can be focally positive, raising the possibility of carcinoma. The tumor cells carry t (1;3) translocation resulting in WWTR1-CAMTA1 fusion gene in about 90% of cases and therefore CAMTA1 immunostaining can be helpful. Other small subsets of cells show YAP1-TFE3 fusion. The latter expresses TFE3 by immunostaining. The differential diagnosis includes epithelioid hemangioma, epithelioid angiosarcoma (the dense sclerosis and hyalinization frequently present in EHE help distinguish it from angiosarcoma and hemangioma), chondrosarcoma (negative vascular markers and positive S100 stain) and sometimes carcinoma.