Which mutation is helpful to differentiate between IPMN and MCN?

• A. GNAS
• B. WT
• C. KRAS
• D. p53

Answer: (A)

The important idea here is that certain molecular changes reflect the biology of different pancreatic cystic neoplasms. A GNAS mutation is a hallmark of IPMN, especially the intestinal type, because activating mutations in GNAS lead to constitutive Gs alpha signaling and the mucinous, papillary nature seen in IPMNs. In contrast, MCNs typically do not have GNAS mutations; they more often show KRAS mutations, but KRAS is not specific because it can be present in both lesions. So finding a GNAS mutation strongly points to IPMN rather than MCN, whereas p53 alterations relate more to higher-grade change rather than distinguishing IPMN from MCN.