Ossifying gastric carcinoid tumor containing bone morphogenetic protein, osteopontin and osteonectin

We report a case of gastric carcinoid tumor with ossification. A 47-yr-old man complaining of abdominal discomfort underwent gastrointestinal endoscopic examination, which revealed a submucosal tumor in his stomach. The tumor was extirpated by endoscopic enucleation. Histologically, the tumor was widely occupied by mature bone tissues, where scattered carcinoid tumor cell nests surrounded bone tissues or located in stromal areas. Immunohistochemically, the tumor cells were strongly positive for cytokeratin, chromogranin A, synaptophysin, neurofilaments and neuron-specific enolase, underscoring the diagnosis of carcinoid tumor. They also stained positive with markers of bone formation and differentiation, such as bone morphogenetic protein, osteopontin and osteonectin. There are only four cases in the world literature, including a current case of ossifying gastric carcinoid tumor, in which the excessive production of peptides promoting ossification was considered to be implicated in the unusual appearance of the bone.