Frequency of Subtypes of Biliary Intraductal Papillary Mucinous Neoplasm and Their MUC1, MUC2, and DPC4 Expression Patterns Differ from Pancreatic Intraductal Papillary Mucinous Neoplasm

Background Biliary intraductal papillary mucinous neoplasm (B-IPMN) has been proposed as a unique clinicopathologic disease with distinct histopathologic features, although wide acceptance remains controversial. A recent consensus conference classified pancreatic IPMN (P-IPMN) into 4 subtypes (ie, gastric, intestinal, pancreatobiliary, oncocytic) based on morphologic appearance and mucin (MUC) staining properties. The aim of this study was to determine whether B-IPMN has similar histopathologic and immunologic subtypes to P-IPMN. Study Design Specific immunostaining for MUC1, MUC2, and deleted for pancreas cancer, locus 4 were performed on specimens from 19 patients with a histopathologic diagnosis of B-IPMN. Immunostaining patterns of B-IPMN were correlated with histopathology. Results Based on histopathology, the following subtypes of B-IPMN were identified: pancreatobiliary n=9 (47%), intestinal n=8 (42%), oncocytic n=2 (11%), and gastric n=0 (0%). Pancreatobiliary and oncocytic subtypes of B-IPMN were positive for MUC1 and negative for MUC2, and intestinal subtypes were positive for MUC2 and negative for MUC1. Thirteen of the 19 B-IPMN were associated with invasive carcinoma; loss of deleted for pancreas cancer, locus 4 was found in 6 of 13 invasive components and in 3 of 19 noninvasive components of B-IPMN. Five-year survival for patients with resected B-IPMN and invasive carcinoma was 38%, which is similar to that for resected P-IPMN with invasive carcinoma. Conclusions Histopathologic subtypes and type-specific MUC expression patterns of B-IPMN resemble those of P-IPMN. MUC1 expression and/or absence of MUC2 expression, which correlate with aggressive features of P-IPMN, were found in B-IPMN and correlate with invasive B-IPMN. Loss of deleted for pancreas cancer, locus 4 parallels the findings observed in P-IPMN. These findings provide additional support that B-IPMN is a unique entity with similarities to main duct P-IPMN.