A case report of primary Kaposiform hemangioendothelioma of the humerus.

To examine the clinicopathological and immunohistochemical features of Kaposiform hemangioendothelioma (KHE) and discuss its differential diagnosis and prognosis. A patient with KHE was examined; the patient's clinical and histopathological features were observed, and the expression levels of CD31, CD34, ERG, D2-40, SMA, GLUT-1, and LANA-1 were assessed. The patient was a four-year-old child with primary KHE of the humerus. She was admitted to the hospital because of pain in the right elbow joint and limited movement for more than 2 years. Imaging revealed Langerhans cell histiocytosis. The child was not diagnosed with Kasabach-Merritt phenomenon (KMP). The tumor consists of multiple hemangiomatous nodules with infiltrative growth separated by fibrous connective tissue. The proliferating hemangiomatoid nodules consisted of crisscrossing short spindle-shaped cell bundles and erythrocyte-containing lacunar or crescentic vessels. Immunohistochemical staining showed that the tumor cells diffusely expressed CD31, CD34, ERG, and other vascular endothelium-derived markers; further, the tumor cells expressed neither GLUT-1 nor LANA-1. The patient's general condition improved after surgical resection. There was no tumor recurrence after more than 8 months of follow-up. Primary KHE of the humerus is a rare vasculogenic tumor. It presents with morphological features that require an accurate differential diagnosis.