A case of primary combined neuroendocrine carcinoma with squamous cell carcinoma in the upper gingiva

Neuroendocrine carcinoma is a rare neoplasm that occurs widely in various organs and tissues. The biological behavior of this tumor in the oral region remains poorly understood. We encountered an extremely rare case of combined neuroendocrine carcinoma with squamous cell carcinoma, occurring at the buccal gingiva in a 62-year-old woman. Left partial maxillectomy was performed. Histological examinations revealed solid nests with extensive necrosis and nuclear palisading at the periphery. The tumor also showed areas of stratified neoplastic squamous differentiation. Immunohistochemically, tumor nests stained positive for synaptophysin, chromogranin, N-CAM (CD56), and neuron-specific enolase. Strong positivity was seen for K14 and K17 in the squamous component and for K7 in the neuroendocrine component. Both components showed K19 staining. Cells with squamous differentiation and K14 staining occasionally expressed p63. The patient showed no evidence of disease as of 23 months postoperatively. Given the aggressive characteristics of neuroendocrine carcinoma, strict follow-up has been performed.