**4. Pathogenesis**

IPMNs are mucinous cystic lesions of the pancreas that are characterized by neoplastic, mucin-secreting, and papillary cells projecting from the pancreatic ductal surface. They arise from the epithelial lining of the main pancreatic duct or its side branches. Intraductal proliferation of mucin-producing columnar cells is the main histologic characteristic of IPMNs, and intraluminal growth causes dilatation of the involved duct and its proximal segment. They are usually found in the head of the pancreas as a solitary cystic lesion, but in 20–30% of the cases, they may be multifocal, and in 5–10% of cases, they may involve the pancreas diffusely [18–20]. In BD-IPMN, malignant tumors can be found in 6–46% and in MD-IPMN in 57–92%, making that MD-IPMN leads to worse prognosis [5].

#### **4.1. Progression to pancreatic cancer**

IPMNs are thought to follow an orderly progression from a benign neoplasm to invasive carcinoma of the pancreas, they range from premalignant lesions with low-grade dysplasia to invasive malignancy, and they have a clear tendency to become invasive carcinoma [5, 21–24]. It has been estimated a 5–6 year progression rate, depending on the subtype. They are graded according to the most atypical area in the lesion as:

