Kaposiform hemangioendothelioma in adults. Clinicopathologic and immunohistochemical analysis of three cases.

Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm that previously has been described only in children. We report three cases occurring in adults. The patients, two men and one woman, were aged 64, 55, and 48 years, respectively. Lesions arose on the chest wall, the lateral aspect of the neck, and in the groin and buttock, and each was situated in superficial soft tissue. Tumor size ranged from 0.9 to 7 cm. Histologically, in all cases a lobular or nodular growth pattern of densely packed spindle-shaped tumor cells closely associated with small slitlike and sievelike blood vessels was seen. Within one lesion, small nodules of plumper, epithelioid tumor cells were identified. Well-formed capillaries frequently containing fibrin thrombi were observed mainly in the periphery of tumor nodules. Areas of hemorrhage and hemosiderin deposits were observed in two cases. Associated lymphangiomatosis composed of diffusely infiltrating lymphatic spaces of the dermis and subcutis was present in one case. Nuclear atypia was minimal in all cases, and mitotic figures were rare in two cases; in one case up to 6 mitoses in 10 high-power fields were noted focally. Immunohistochemically, well-formed capillaries stained positively for all the vascular markers used; however, endothelial cells lining the small slitlike and sievelike vascular spaces did not stain for von Willebrand factor. At least focally, actin-positive pericytes were seen. Neoplastic spindled cells stained only focally for CD34 and CD31. Two lesions were excised with clear margins; in one case only repeated biopsies were done. Follow-up information between 14 and 28 months revealed no sign of recurrence or metastasis. In adults, the differential diagnosis of KHE comprises especially Kaposi's sarcoma and spindle cell hemangioendothelioma; further differential diagnoses include tufted hemangioma and cellular capillary hemangioma, which occur rarely in adults.