Clinico-pathological features and prognosis of mixed-IPMNs with a focal involvement of the main pancreatic duct

Intraductal papillary mucinous neoplasms (IPMNs) involving both branch ducts and the main pancreatic duct (MPD), known as Mixed-IPMNs, generally behave like main duct (MD-) IPMNs. However, a subgroup of Mixed-IPMNs with minimal involvement of MPD (Min–Mix IPMN) has been described. Aim of this study was to analyse the biological behaviour of patients with Min–Mix IPMNs. Retrospectively collected data from all patients resected for pathologically confirmed IPMN at San Raffaele Hospital between 2009 and 2019 was prospectively analysed. Demographic, perioperative and survival data was analysed, comparing Min–Mix-IPMNs with other IPMNs. Among 464 patients included, 35 Min–Mix IPMNs were identified. When compared with MD and “typical” mixed-IPMNs, patients were younger, less frequently presented altered Ca19.9 or jaundice at diagnosis (p = 0.006). Most Min–Mix IPMNs presented only worrisome features, like BD-IPMNs (71% and 67% respectively), versus 87% and 73% high-risk stigmata in MD/Mixed-IPMNs (p < 0.001). At pathology, Min–Mix IPMNs showed low-grade dysplasia in 74% of cases (p < 0.001 versus MD and Mixed-IPMN). 5-year overall survival was higher for BD and Min–Mix-IPMN compared with MD and Mixed-IPMNs. Likewise, 5-year event free survival was statistically higher for Min–Mix than MD-IPMNs. This study confirms a subgroup of Mixed-IPMNs with minimal involvement of the MPD at pathology which manifests characteristics and behaviour more like BD than MD/Mixed-IPMNs.