Large cell neuroendocrine carcinoma of the ileocecal junction with well differentiation adenocarcinoma.

: Neuroendocrine tumors are unique and rare tumors originating from neuroendocrine cells. Large cell neuroendocrine tumors have been found in almost every organ such as gastrointestinal tract, bronchopulmonary, pancreas, uterine cervix, urinary bladder and salivary gland, but primary sites in gastrointestinal tract and lung are the most frequent. These neoplasms show neuroendocrine differentiation in organizational structure, which requires further confirmation with immunohistochemistry or electron microscope. In immunohistochemistry staining, pure neuroendocrine areas are diffusely stained positive for synaptophysin (Syn), chromogranin (CgA) and CD56.At least two neuroendocrine markers (Syn, CgA or CD56) must be diffusely stained positive to establish a diagnosis for large cell neuroendocrine carcinoma. We studied a rare case of large cell neuroendocrine tumor that was originated from the ileocecal junction and showed CgA, Syn and CD56 triple-negative. The tumor, however, showed typical morphologic and immunohistochemical features of neuroendocrine differentiation; it also exhibited well differentiation and a significant peritumoral lymphoid reaction. Furthermore, we also found the intracytoplasmic neurosecretory granules through the electron micrograph examination.