Mixed adenoneuroendocrine carcinoma of the tongue arising within a congenital enteric cyst

Background Primary intestinal‐type adenocarcinoma of the tongue is rare. This represents the first reported case of a primary mixed adenoneuroendocrine carcinoma (MANEC) of the tongue arising within a congenital enteric cyst. Methods A 52‐year‐old man presented with a midline tongue mass that was connected to the mucosal surface with an epithelial‐lined sinus tract. Morphological examination and immunohistochemical profiling of the neoplasm were performed. Results Histopathological evaluation showed a primary MANEC arising within a preexisting congenital enteric cyst, comprising both adenocarcinoma and neuroendocrine components. The adenocarcinoma had a colonic‐type morphology and coexpressed CK7, CK20, and CDX2. Imaging and colonoscopy excluded a distant primary colorectal neoplasm. Conclusion The association of primary MANEC of the tongue with a gastrointestinal heterotopic cyst supports an origin from entrapped endodermal elements as opposed to salivary duct origin. This case raises the awareness of a rare yet prognostically important complication of a gastrointestinal heterotopic cyst.