What is the cyst marker profile for a mucinous cystic neoplasm (MCN)?

• A. KRAS mutation, low amylase, high CEA
• B. KRAS mutation, high amylase, high CEA
• C. GNAS mutation, high amylase, low CEA
• D. No mutation, high amylase, high CEA

Answer: (A)

Understanding how cyst fluid markers help distinguish pancreatic cysts is key. Mucinous cystic neoplasms (MCNs) typically behave like mucinous lesions, so their fluid commonly shows a mucinous signature: a KRAS mutation is frequently present, CEA is elevated, and amylase is low because MCNs usually do not communicate with the pancreatic duct.

So the best profile matches KRAS mutation with high CEA and low amylase. The elevated CEA supports a mucinous content, while low amylase indicates no ductal communication, which is characteristic of MCN rather than a pseudocyst or IPMN. GNAS mutations are more characteristic of IPMNs, which often have different ductal involvement and amylase patterns. High amylase would suggest ductal communication, which is not typical for MCN.