Which laboratory tests should be monitored in a patient with intraductal papillary mucinous neoplasm (IPMN)?

Laboratory Monitoring in IPMN

Serum CA 19-9 should be measured routinely in all patients with IPMN, as elevated levels >37 U/mL are strongly associated with invasive carcinoma and serve as a relative indication for surgical resection. 1

Essential Laboratory Tests

CA 19-9 (Primary Tumor Marker)

• Measure at baseline evaluation in all patients with radiologically suspected IPMN 1
• Threshold for concern: >37 U/mL (in the absence of jaundice) 1
• Clinical significance: CA 19-9 >37 U/mL has 74% positive predictive value and 81.7% accuracy for identifying invasive IPMN 1
• Prognostic value: Elevated CA 19-9 is associated with worse overall survival (HR=1.943) and disease-free survival (HR=2.484) 2
• Important caveat: 74% of patients with invasive IPMN have elevated CA 19-9, while only 14% with non-invasive tumors show elevation 3
• Combined markers: 80% of invasive IPMNs have elevated CA 19-9 and/or CEA, compared to only 18% of benign lesions 3

Glucose Metabolism Monitoring

• Fasting blood glucose and/or HbA1c should be tested routinely during surveillance 1
• New-onset diabetes mellitus is a relative indication for surgery and associated with malignant transformation 1
• Clinical context: New-onset diabetes in the setting of IPMN warrants heightened concern for malignant progression 1

CEA (Limited Utility in Serum)

• Serum CEA has minimal utility for IPMN management and does not correlate reliably with malignancy 2
• Note: This differs from cyst fluid CEA (≥192 ng/mL), which helps distinguish mucinous from non-mucinous cysts 4
• Combined assessment: While serum CEA alone is not predictive, the combination of elevated CA 19-9 and/or CEA increases detection of invasive disease 5, 3

Surveillance Algorithm Based on Laboratory Findings

When CA 19-9 is Elevated (>37 U/mL)

• Consider this a relative indication for surgery, particularly when combined with other worrisome features 1
• Reassess imaging with MRI/MRCP and/or EUS to evaluate for absolute surgical indications 1
• Shorten surveillance interval to 3-6 months if surgery is not immediately indicated 1

When CA 19-9 is Normal (≤37 U/mL)

• Continue standard surveillance at 12-month intervals if no other concerning features present 1
• Maintain routine glucose monitoring to detect new-onset diabetes 1

Post-Resection Monitoring

• Lifelong follow-up required even after partial pancreatectomy due to risk of metachronous lesions 1
• Continue CA 19-9 monitoring in the remnant pancreas surveillance protocol 1

Common Pitfalls to Avoid

• Do not use elevated CA 19-9 as the sole indication for surgery—it must be interpreted alongside imaging features 1
• Remember that CA 19-9 can be falsely elevated in jaundice—the >37 U/mL threshold applies only in the absence of biliary obstruction 1
• Do not rely on serum CEA alone—it lacks predictive value for IPMN malignancy unlike its role in cyst fluid analysis 2
• CA 19-9 does not predict high-grade dysplasia—it specifically correlates with invasive carcinoma, not dysplasia alone 2