Kaposi-like vascular tumor of the urinary bladder in a cow

Kaposiform hemangioendothelioma is a rare human vascular neoplasm. In veterinary medicine this tumor type was only recognized in the dog. Here we describe an unusual case arising in the urinary bladder of a Holstein-Friesian adult cow. Histologically the tumor presented a nodular proliferation of spindle cells, forming angular slits, often containing extravasated erythrocytes. Peripherically, well-formed vascular channels were seen. These cells were positive to vimentin and to factor VIII-related antigen by immunohistochemical stain. Based on its characteristics, it was classified as kaposiform hemangioendothelioma and as far as we know, it is the first case described in cattle.