Duodenal sessile serrated adenoma/polyp with characteristic endoscopic and pathologic features

Sessile serrated adenomas/polyps (SSA/Ps), recently called sessile serrated lesions, have a neoplastic pathway in the large intestine and are treated as lesions with malignant potential. There are a few reports of traditional serrated adenomas in the duodenum but no reports of duodenal SSA/Ps. A 66-year-old man underwent screening upper gastrointestinal endoscopy and was found to have a white elevated lesion in the second portion of the duodenum. Magnifying blue laser imaging showed various sized villous-like structures with dilated crypt openings in the white surface mucosa, similar to a SSA/P. Based on these images, a duodenal adenoma was suspected at the time of endoscopic resection. Pathological findings of the resected specimen showed a saw-tooth structure corresponding to basal crypt dilatation and branching with mucus and positive immunostaining for MUC6 and MUC2, similar to a colonic SSA/P. MUC5AC did not stain the glandular crypt cells. KRAS mutation was detected. Immunohistochemical expression of Annexin A10 was clearly identified in the lesion. Although not all of molecular biological features were satisfied, these findings were similar to a colonic SSA/P which has malignant potential. This is the first report of a duodenal SSA/P which should be considered when evaluating elevated duodenal lesions.