What is CA (Cancer Antigen) 19-9 and its role in managing a patient with suspected pancreatic cancer?

From the Guidelines

CA 19-9 is a tumor marker that plays a crucial role in the management of pancreatic cancer, particularly in supporting diagnosis, providing baseline information, and monitoring treatment response and disease recurrence. It is a carbohydrate antigen that can be detected in blood serum and is elevated in approximately 70-80% of patients with pancreatic cancer 1. While CA 19-9 is not recommended as a screening test for the general population due to limited sensitivity and specificity, it is useful in the clinical setting when combined with imaging studies like CT or MRI 1.

Key Points about CA 19-9

• CA 19-9 is not specific for pancreatic cancer and can be elevated in non-cancerous conditions like pancreatitis, liver disease, and biliary obstruction 1.
• About 5-10% of the population lacks the Lewis antigen necessary to produce CA 19-9, resulting in false-negative results even in the presence of cancer 1.
• CA 19-9 provides valuable baseline information before treatment begins and serves as an important tool for monitoring treatment response and disease recurrence 1.
• Decreasing levels of CA 19-9 often indicate effective therapy, while rising levels suggest disease progression 1.

Clinical Use of CA 19-9

• CA 19-9 should always be interpreted in the context of clinical findings and imaging studies rather than as a standalone diagnostic test 1.
• The use of CA 19-9 in combination with imaging studies and clinical findings can help support the diagnosis of pancreatic cancer and guide treatment decisions 1.
• CA 19-9 can be used to monitor treatment response and detect disease recurrence, allowing for timely adjustments to treatment plans 1.

Limitations and Considerations

• CA 19-9 is not recommended for screening the general population due to its limited sensitivity and specificity 1.
• False-positive results can occur due to non-cancerous conditions, and false-negative results can occur in individuals lacking the Lewis antigen 1.
• CA 19-9 levels should be interpreted with caution and in the context of the overall clinical picture 1.

From the Research

What is CA 19-9

• CA 19-9, also known as carbohydrate antigen 19-9 or cancer antigen 19-9, is a serum tumor marker used in the diagnosis and management of pancreatic cancer 2, 3, 4, 5.
• It is normally synthesized by normal human pancreatic and biliary ductal cells, as well as by gastric, colon, endometrial, and salivary epithelia 2.
• CA 19-9 is present in small amounts in serum and can be overexpressed in several benign gastrointestinal disorders, but it exhibits a dramatic increase in its plasmatic levels during neoplastic disease 2.

Role of CA 19-9 in Managing a Patient with Suspected Pancreatic Cancer

• CA 19-9 is the most commonly used and best-validated serum tumor marker for pancreatic cancer diagnosis in symptomatic patients and for monitoring therapy in patients with pancreatic adenocarcinoma 2, 3, 4.
• The sensitivity and specificity of CA 19-9 for the diagnosis of pancreatic cancer in symptomatic patients are 79-81% and 82-90%, respectively 3, 4.
• Pre-operative CA 19-9 serum levels can provide useful prognostic information, with patients having normal levels (<37 U/mL) having a prolonged median survival compared to those with elevated levels (>37 U/mL) 3, 4.
• A CA 19-9 serum level of <100 U/mL implies likely resectable disease, whereas levels >100 U/mL may suggest unresectability or metastatic disease 3, 4.
• Normalization or a decrease in post-operative CA 19-9 serum levels by ≥20-50% from baseline following surgical resection or chemotherapy is associated with prolonged survival 3, 4.
• CA 19-9 can also be used to assess response to chemotherapy, with a decline in CA 19-9 levels indicating a positive response to treatment 6.

Limitations of CA 19-9

• CA 19-9 has several limitations, including poor sensitivity, false negative results in Lewis negative phenotype (5-10%), and increased false positivity in the presence of obstructive jaundice (10-60%) 2, 3, 4.
• Non-specific expression in several benign and malignant diseases, false negative results in Lewis negative genotype, and an increased false positive results in the presence of obstructive jaundice severely limit the universal applicability of serum CA 19-9 levels in pancreatic cancer management 3, 4.
• CA 19-9 is not useful as a screening marker for asymptomatic populations due to its low positive predictive value (0.5-0.9%) 4.