Intraductal papillary mucinous neoplasm (IPMN) of the gastric-type with focal nodular growth of the arborizing papillae: a case of high-grade transformation of the gastric-type IPMN.

We present a case of intraductal papillary mucinous neoplasm (IPMN) of the pancreas, demonstrating a process of high-grade transformation of the gastric-type IPMN. An 83-year-old Japanese woman underwent pylorus-preserving pancreatoduodenectomy for removal of a multicystic mass of the pancreas head, which had been followed up for 7 years. The removed tumor was a low-grade gastric-type IPMN spreading in the branch ducts, focally forming an intraluminal nodular lesion. The nodular lesion was comprised of arborizing papillotubular proliferation of cuboidal to columnar epithelia with high-grade atypia, and was characterized by diffuse MUC1 expression and a gastric mucin phenotype (focal MUC5AC and MUC6 expressions). Therefore, the nodular lesion was consistent with the pancreatobiliary-type IPMN, and the present case suggests that the low-grade gastric-type IPMN may progress to a focal intraductal carcinoma over the years, and the pancreatobiliary-type IPMN may be one of the forms of such high-grade transformation of the gastric-type IPMN. One of the cystic lesions was an oligocystic-type serous cystic neoplasm (serous cystadenoma), which might be an incidental concomitance or have a common basis.