A case of combined large cell neuroendocrine carcinoma of the lower gingiva associated with focal differentiation to squamous cell carcinoma.

An extremely rare case of combined large cell neuroendocrine carcinoma of the lower gingiva associated with focal differentiation to squamous cell carcinoma is presented. Travis et al. proposed a new, distinctive clinicopathologic type of pulmonary neuroendocrine tumor, termed large cell neuroendocrine carcinoma(LCNEC). It is defined as a poorly differentiated, high-grade neuroendocrine tumor that has morphologic and biologic features intermediate between atypical carcinoid and small cell carcinoma.A 59-year-old man presented with bleeding and swelling of the lower gingiva. The pathological diagnosis of a biopsy specimen was poorly differentiated squamous cell carcinoma. The patient therefore underwent surgical resection of the tumor.The tumor was composed of larger cells than those of small cell carcinoma and exhibited solid, trabecular, and slightly rosette-like growth patterns with a high mitotic rate in normal subepithelial interstitial tissue. Grimelius staining was positive, and chromogranin A and neural cell adhesion molecule (CD56)immunostaining was positive. The tumor was diagnosed as large cell neuroendocrine carcinoma on microscopic and immunohistochemical studies.On hematoxylin and cosin staining, there were no signs of transition between neuroendocrine carcinoma and carcinoma in situ. However, at the circumference of neuroendocrine carcinoma, a mass of cells associated with differentiation to squamous cell carcinoma was seen. These cells showed positive CAM5.2(lowmolecular-weight cytokeratin)immunostaining. Therefore, the tumor was finally diagnosed as a combined large cell neuroendocrine carcinoma of the lower gingiva associated with focal differentiation to squamous cell carcinoma.