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Large cell neuroendocrine carcinoma (LCNEC) is a poorly differentiated that typically arises in the lung. Because of its rarity and poor prognosis, standardized treatment has not been established yet. A 53-year-old male was initially diagnosed as maxillary sinus squamous (SCC) arising from inverted papilloma (clinical stage T4bN2bM0, IVb), underwent concurrent chemoradiotherapy. After achieving complete remission for 3 years, recurrent tumors were found, whom pathologic diagnosis turned out to be LCNEC. He endoscopic transnasal tumor extirpation, followed by adjuvant Until postoperative 12 months, he showed no evidence recurrence. To best our knowledge, this first report SCC transformed LCNEC after Key words: Carcinoma, neuroendocrine; ㆍ Cell transformation, neoplastic Chemoradiotherapy Maxillary neoplasm Papilloma,