2.2. Pathologic examination

In this retrospective study, the term malignant is used as defined in the 2017 guidelines and includes such conditions as invasive carcinoma and high-grade dysplasia. The latter term has been preferred to “carcinoma in situ” and should be abandoned as outlined in the WHO classification [16]. Each histological subtype defined by Furukawa in 2003 has a specific description. There are four distinct subtypes based on morphological and immunohistochemical features: gastric, intestinal, pancreatobiliary, and oncocytic. For example, gastric subtype IPMNs usually have low-grade dysplasia while other subtypes are more likely to develop high-grade dysplasia [7].