**5. Mucinous cystic neoplasms (MCNs)**

These are the most frequent cystic pancreatic neoplasms. They amount for 20–40% of all cystic tumors with the prevalence of 25–30% for mucinous cystadenoma and 15% for mucinous cystadenocarcinoma.

There are two types of MCNs, both not communicate with the pancreatic duct. The cysts are lined by columnar, mucin‐producing ductal epithelium and sometimes papillary epithelium. In the first type, ovarian‐type stroma is located under the epithelial layer; the ovarian‐type stroma is positive to estrogen and progesterone receptors [6]. Ectopic ovarian stroma can be included in the pancreas during embryogenesis and this can cause, by releasing hormones, the proliferation of epithelium and then the cystic neoplasm. This hypothesis that connects the stromal component of MCNs and ovarian tissue should be supported by morphological resemblance. This type is present almost exclusively in women of fifth–sixth decade and predominantly is located in body and tail of pancreas.

There is another type of MCNs, more common, without ovarian stroma that can be located anywhere in the pancreas and occurs in both sexes. The malignant potential is very high in MCNs based on the possible evolution of mucinous transitional epithelium. Consequently, MCNs may be classified based on the degree of dysplasia: MCNs with low‐intermediate grade dysplasia, with high‐grade dysplasia, and finally with associated invasive carcinoma [14]. Histological heterogeneity of MCNs is in evidence with coexistence of benign appearance and malignant epithelia. Malignancy, *in situ* or invasive, is found in 35–45% of cases [21].

The macroscopic appearance of MCNs is cystic mass, unilocular or multilocular, containing thick mucine or sometimes mixed with hemorrhagic materials. The cystic wall is well defined, fibrous, and sometimes (10%) calcified.

Clinical appearance in the symptomatic patients presents abdominal pain, palpable mass, anorexia, fatigue, weight loss, and in some cases pancreatitis. The results of routine laboratory examinations are generally non‐specific. One‐third of patient can be asymptomatic [22]. Imaging examinations (CT and MRI) of MCNs show large cysts with septae and in some cases peripheral thin calcification of the walls. In some experiences, the presence of peripheral calcification, wall thickening, and thick septation has been highlighted as important for malignant evolution of MCNs [23]. Overlappable data can be detected by EUS: mass formed from fluid‐filled cysts with thin walls, septae, and diameter 1–2 cm without duct communica‐ tion. Malignancy suspicious can be based on wall thickening, irregularity, intracystic solid mass, and increased size of all lesion.

EUS‐FNA can allow the evaluation of fluid content of cysts: CEA levels are high and can be useful in the diagnosis [6]. Pathological and evolutionary characteristic of MCNs affect treatment decisions. Malignant potential of these neoplasms is the cornerstone of the therapy. Relevant is the increase in the frequency of K‐ras and p53 mutations as in sequence adenoma– carcinoma of colon cancer. Consequently, there is high likelihood of evolution into cancer if untreated. In fact, there is age difference of 10 years longer between patients with cystadeno‐ carcinoma and patients with cystadenoma [24, 25]. Based on the pathological characteristics of histologic heterogeneity, extensive histologic sampling is necessary for certainty of diagnosis (from adenoma to carcinoma). The current and unanimous guidelines propose the surgical treatment for all MCNs. The contraindications for intervention are related to the patient's conditions. The pancreatic resection is connected with the location of lesion: head, body, and tail. Duodenopancreatectomy, middle pancreatectomy, and distal pancreatectomy with or without splenectomy should be performed. Less extensive resections, such as enucleations are not recommended also because usually followed by high complications rate. Laparoscopic approaches are becoming more common and fully justified.

Cure rate of surgical resection for non‐invasive MCNs (carcinoma *in situ*) is 100%. The 5‐year survival rate for resected patients with invasive lesions is 40–50%; whereas the 2‐year survival rate is 60–70%. Surveillance after surgery in these patients is required.
