CD10-positive malignant spindle cell tumor of the lip in a child: a malignant myoepithelioma?

A 9-year-old girl consulted to our hospital because of lower lip tumor. Excision of the tumor was performed. Histologically, the tumor consisted of cellular spindle and round cells with hyperchromatic nuclei and nucleoli. Mitotic figure and apoptotic bodies were scattered. Immunohistochemically, the tumor cells were strongly and diffusely positive for CD10 and vimentin. The tumor was focally positive for S100 protein, α-smooth muscle actin, PDGFRA, HER2/neu, p53, and CD68. The Ki-67 labeling was 20%. In contrast, the tumor cells were negative for pancytokeratins (AE1/3, CAM5.2, WSS, KL-1, HNF116), cytokeratin (CK) 5/6, CK34βE12, CK7, CK8, CK14, CK18, CK19, CK20, EMA, desmin, CD34, melanosome, KIT, p63, myoglobin, CD45, CD56, GFAP, D2-40, CEA and synaptophysin. The Histologies, positive p53 protein, and Ki-67 labeling of 20% suggested low grade malignancy. Although histological type was unclear, the author diagnosed this tumor as malignant myoepithelioma arising from the lip minor salivary gland because of positive reaction for S100 protein, α-smooth muscle actin, and CD10. The patient is now free from tumor 8 years after the first presentation.