Malignant potential and specific characteristics of pure main duct type intraductal papillary mucinous neoplasm

Background As the malignant potential of main duct (MD-) type intraductal papillary mucinous neoplasm (IPMN) has been discussed together with Mixed-type in most previous studies, the malignant potential of pure MD-type IPMN remains unclear. This study evaluated the specific characteristics and predictors of high-grade dysplasia (HGD) and invasive intraductal papillary mucinous carcinoma (IPMC) for pure MD-type IPMN. Methods From 1,100 patients with IPMN, this study includes 387 patients that underwent surgery. We evaluated the specific characteristics of pure MD-type IPMN by comparing clinicopathological factors between MD-type (n = 79) and branch duct (BD-) type (n = 146) or Mixed-type IPMN (n = 162), and predictors of HGD/invasive IPMC in pure MD-type IPMN. Results The rate of HGD/invasive IPMC was significantly higher in MD-type than in BD-type (70.9 vs. 48.6%, P = 0.001), although there was no difference between MD-type and Mixed-type IPMNs (P = 0.343). Recurrence-free survival (RFS) and disease-specific survival (DSS) of patients with MD-type were better than those of patients with Mixed-type (P = 0.008 and P = 0.009, respectively). There were no significant differences in RFS, overall survival, and DSS between patients with MD-type and patients with BD-type IPMNs. Multivariate analysis showed two independent predictors of HGD/invasive IPMC in MD-type IPMN; mural nodule height ≥5 mm (P = 0.025, odds ratio [OR]; 16.949) and carcinoembryonic antigen (CEA) level in the pancreatic juice obtained by preoperative endoscopic retrograde pancreatography ≥50 ng/ml (P = 0.039, OR; 9.091). Conclusions Measurement of mural nodule height and CEA in the pancreatic juice might be useful in determining surgical indication for pure MD-type IPMN, although further studies for confirmation are essential.