Invasive carcinoma derived from “flat type” branch duct intraductal papillary mucinous neoplasms of the pancreas: impact of classification according to the height of mural nodule on endoscopic ultrasonography

Background It has been reported that many branch duct intraductal papillary mucinous neoplasms ( BD ‐ IPMN ) with a mural nodule ( MN ) reveal adenocarcinomas. On the other hand, invasive cancer derived from BD ‐ IPMN without MN on endoscopic ultrasound ( EUS ) also exists. The aim of this study was to elucidate the clinicopathological features of invasive cancer derived from BD ‐ IPMN without MN on EUS . Methods Twenty‐one patients pathologically diagnosed with invasive cancer derived from BD ‐ IPMN were included in this study. Results Based on the height of MN s on EUS , the subjects could be clearly classified as 12 patients whose background BD ‐ IPMN s had high MN s (nodule‐forming type IPMN ) and nine whose background BD ‐ IPMN s showed no MN s (flat type IPMN ). The background BD ‐ IPMN of the 12 patients with nodule‐forming type IPMN were non‐gastric type. On the other hand, the background BD ‐ IPMN of the nine patients with flat type IPMN was gastric type. The recurrence rate was higher (33% vs. 67%) and the 5‐year survival was worse (76% vs. 33%) in flat type IPMN . Conclusions There may be a pathway for the development of invasive cancer without the formation of an MN in BD ‐ IPMN , and attention should be paid even to the patients with BD ‐ IPMN which does not present an MN .