Mucinous Cystic Neoplasms Lined by Abundant Mucinous Epithelium Frequently Involve KRAS Mutations and Malignant Progression.

Background: Pancreatic and hepatic mucinous cyst neoplasms (MCNs) have a malignant potential, but indolent MCNs are not uncommon. Materials and Methods: The pathological and genetic characteristics of resected MCNs (n= 15) categorized by the amount of mucin of the lining epithelium were investigated. Results: MCNs were divided into two groups: (i) a rich (r)-MCN group (n= 6), in which more than half of the epithelium was lined by abundant mucinous epithelium; and (ii) a poor (p)-MCN group (n= 9), which consisted of the remaining cases. Three patients in the r-MCN group showed invasive carcinoma or high-grade dysplasia, whereas all patients in the p-MCN group showed low-grade dysplasia. Mutations of Kirsten rat sarcoma viral oncogene homolog (KRAS) were more frequent in the r-MCN group (83%) (p-MCN; 11%, p< 0.05). Conclusion: Mucinous MCNs more frequently have KRAS mutations and higher risk of malignant progression.