Dynamic Predictors of Malignancy in Main Duct-Involved IPMN: The Critical Role of MPD Diameter Changes in a Multicenter Study

Background and Aim: Main pancreatic duct (MPD)-involved intraductal papillary mucinous neoplasms (IPMNs) carry a significant risk of malignant transformation. However, the long-term malignancy outcomes and the effects of dynamic changes in MPD diameter and other dynamic predictors remain poorly understood. Methods: This multicenter retrospective cohort study included patients diagnosed with MPD-involved IPMNs between 2010 and 2023 at eight university hospitals in South Korea. All patients underwent surveillance every 6 to 12 months, which included clinical assessments, tumor marker testing, and imaging studies. Malignancy was confirmed through surgical pathology, endoscopic tissue acquisition, or evidence of radiologic progression. Results: Among 168 patients, 30 (17.8%) developed malignancy during a median 4.0-year follow-up (IQR, 2.1–7.0), yielding an annual incidence of 4.5%. Cumulative incidences of malignancy were 7.7% at 2 years, 14.3% at 4 years, and 14.9% at 6 years. The strongest predictor of malignancy was an MPD growth rate ≥ 2 mm/year (odds ratio [OR]: 33.039, p < 0.001), which also remained significant in Cox regression (hazard ratio: 45.356, p < 0.001). The emergence of new worrisome features (OR: 3.849, p = 0.036) and high-risk stigmata (OR: 3.288, p = 0.036) were also associated with malignancy risk, though not independently significant in Cox regression. Conclusions: Dynamic MPD monitoring is essential for assessing malignancy risk in patients with MPD-involved IPMN. An MPD growth rate of ≥ 2 mm/year was the strongest predictor of malignant transformation, underscoring the value of longitudinal surveillance over static MPD diameter thresholds. Patients with rapid MPD growth should be considered for early surgical intervention or intensified monitoring to improve clinical outcomes.