Prediction of malignancy in main duct or mixed-type intraductal papillary mucinous neoplasms of the pancreas

Background/Purpose Surgical indications of main duct-involved intraductal papillary mucinous neoplasm (IPMN), especially for main pancreatic duct (MPD) of 5-9 mm, remain controversial. We aimed to predict malignancy risk of main duct-involved IPMN. Methods Total 258 patients with main duct-involved IPMN between 2000 and 2017 in our institute were retrospectively analyzed. Main duct IPMN was classified into segmental and diffuse-type by dilated MPD pattern. Clinicopathologic features and predictive factors for malignancy were analyzed. Results Among 258 patients, 47 and 211 had pure main duct (segmental: 27, diffuse type: 20) and mixed type, respectively. Malignant IPMN presented higher in main duct type (66.0%) compared to mixed type (46.9%). The diffuse type (72.2%) had more invasive carcinoma than the segmental type (40.7%). Invasive IPMN risk increased proportionally to the MPD diameter (5 <= MPD <10 mm vs 10 <= MPD < 15 mm vs MPD >= 15 mm; 23.4% vs 40.0% vs 48.6%). Symptoms, elevated serum carbohydrate antigen, MPD >= 10 mm, mural nodule, thickened wall, and distal atrophy were independent predictive factors for malignancy. Patients with MPD of 5-9 mm with at least one predictive factor had 35.0% of malignancy risk. Conclusions The invasive IPMN risk was different according to the dilated main duct pattern. Patients with main duct type, diffuse type, MPD >= 10 mm, and MPD 5-9 mm with at least one predictive factor should be candidates for immediate surgery.