Composite hemangioendothelioma: clinical and histologic features of an enigmatic entity.

Composite hemangioendotheliomas are rare vascular neoplasms of intermediate biological potential, characterized by a complex admixture of benign, low-grade malignant, and malignant vascular components. They can affect both adults and children, and occur predominantly as long-standing lesions in the dermis and subcutis of the extremities, but have also been increasingly reported at other sites, including the oral cavity and in viscera such as kidney and spleen. These usually behave in a low-grade manner, with a relatively high rate of local recurrence and rarely lymph node and distant metastases, but no tumor-related deaths have been reported. Microscopically these are heterogenous neoplasms with merging of different vascular patterns, which immunohistochemically variably express vascular endothelial markers. Because of the wide morphologic spectrum, they can be difficult to recognize, but accurate diagnosis is crucial for correct treatment and prognostication. We review the literature, discussing clinical and histopathologic features, and the differential diagnosis of these rare tumors.