Thyroid Diseases Associated with Elevated CA 19-9 Levels
Papillary thyroid carcinoma is the most common thyroid disease associated with elevated CA 19-9 levels, with immunohistochemical studies showing CA 19-9 positivity in up to 58% of papillary carcinomas. 1
Malignant Thyroid Conditions with Elevated CA 19-9
- Papillary thyroid carcinoma can express CA 19-9, which may be detected in serum and on immunohistochemical staining of tumor tissue 1, 2
- Anaplastic transformation from papillary thyroid carcinoma has been associated with increased serum CA 19-9 levels, which may serve as a prognostic indicator for this aggressive transformation 3
- Medullary thyroid cancer with advanced disease can present with elevated CA 19-9 levels, which has been identified as an independent predictor of mortality (OR=3.78, P=0.04) 4
- Metastatic papillary thyroid carcinoma can present with elevated serum CA 19-9 levels, particularly in cases with liver metastasis 2
Inflammatory Thyroid Conditions with Elevated CA 19-9
- Subacute granulomatous (de Quervain's) thyroiditis demonstrates CA 19-9 expression in all cases when examined immunohistochemically, with the strongest staining observed in late-stage disease 5
- Focal lymphocytic thyroiditis has shown CA 19-9 expression in immunohistochemical studies 5
- Hashimoto's thyroiditis has demonstrated CA 19-9 positivity on immunohistochemical examination 5
Clinical Significance and Diagnostic Considerations
- CA 19-9 is not typically used as a primary diagnostic marker for thyroid disease, as it lacks specificity and can be elevated in multiple benign and malignant conditions 6, 7
- Serum CA 19-9 levels may serve as a surrogate marker for papillary thyroid carcinoma in place of serum thyroglobulin (Tg) in patients with positive anti-thyroglobulin antibodies, if the primary tumor and/or metastatic lesions are positive for CA 19-9 staining 2
- The American College of Gastroenterology recommends considering CA 19-9 levels in the context of other clinical and diagnostic findings, as elevated levels can be seen in various conditions 8
Important Caveats and Pitfalls
- CA 19-9 is not tumor-specific and should not be used alone for diagnosis of thyroid malignancy 7
- Approximately 5-10% of the population is Lewis antigen negative and cannot produce CA 19-9, making testing ineffective in these individuals 7, 8
- Biliary obstruction is a major cause of false-positive CA 19-9 results, occurring in 10-60% of cases 7
- CA 19-9 measurements using different testing methods cannot be directly compared 8
Monitoring and Management Implications
- In patients with known thyroid cancer and elevated CA 19-9, the marker may be useful for monitoring disease progression and response to treatment 2, 3
- Persistently elevated CA 19-9 levels after treatment may indicate residual disease or recurrence, particularly in papillary thyroid carcinoma cases that express this marker 2
- Elevated CA 19-9 in medullary thyroid cancer patients identifies those with a higher risk of mortality in the short term 4