Primary Duodenal Adenocarcinoma Expressing Carbonic Anhydrase IX

Primary duodenal adenocarcinoma is a rare malignancy whose carbonic anhydrase IX (CA9) expression remains poorly understood. A 73-year-old man visited our hospital for a medical checkup. Transnasal endoscopy revealed a submucosal, tumor-like lesion with a central depression located in the descending part of the duodenum on white light imaging. On texture and color enhancement imaging mode 1, the lesion was highlighted as a reddish, elevated lesion with an irregular mucosa in its central depressed area. Pancreaticoduodenectomy was performed on the suspicion of duodenal adenocarcinoma for biopsy and endoscopic diagnosis, which led to the lesion being diagnosed as tubular adenocarcinoma, pT1b (SM). Immunohistological staining revealed an adenocarcinomatous component positive for CA9, as well as a normal duodenal mucosa. To our knowledge, this report is among the first to describe CA9-expressing primary duodenal adenocarcinoma.