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• KRAS

• resembling luteinized cells

• Low-grade MCNs are characterized by mild to moderate atypia and may or may not reveal papillary projections and mitoses

• cyst-forming and mucin-producing epithelial neoplasm associated with distinctive ovarian-type subepithelial stroma

• body or tail of the pancreas

• women

• s 48 years

• associated invasive carcinoma include large tumour size (> 5 cm), irregular thickening of the cyst wall, intracystic mural nodules, and elevated serum CA19-9 level

• activating mutations in codon 12 of

• cystic mass with a fibrous wall of variable thickness, occasionally containing calcification

• thick mucin and/or haemorrhagic, necrotic material

• cysts of MCNs are lined by epithelium and have underlying ovarian-type stroma

• High-grade MCNs display severe atypia, with the formation of papillae with irregular branching and budding, nuclear stratification with loss of polarity, pleomorphism, and prominent nucleoli; mitoses are numerous

• The distinctive ovarian-type stroma consists of densely packed spindle-shaped cells with round or elongated nuclei and sparse cytoplasm, and its presence is required for the diagnosis

• 15% of MCNs have an associated invasive carcinoma component

• CK7, CK8, CK18, CK19, EMA, CEA, and MUC5AC

• ovarian-type stroma expresses SMA, MSA, desmin, PR (60–90%), and ER (30%)

• MCNs do not grow within the pancreatic duct system, and they contain (by definition) ovarian-type stroma

• carcinomas in MCNs may lose the expression of SMAD4

• and express EMA (MUC1)