CD99 and neoplasm: Immunohistochemical staining showed that epithelial regional tumor cells CK (AE1/AE3), CK7, CAM5.2, and EMA were all positive, expressing CD56 and CD10 to varying degrees, and some cases expressed CK8 and CK18, but CK20 was usually negative; mesenchymal regional tumor cells were positive for Vimentin, CD56, and CD10 and expressed CD99 to varying degrees.