The tissue expression pattern of CA 19.9 is associated with oncological features in medullary thyroid carcinoma.

PURPOSE Elevated serum levels of carbohydrate antigen 19.9 (CA19.9), a well-established tumor marker in pancreatic neoplasms, has been proposed as a prognostic marker of tumor aggressiveness in medullary thyroid carcinoma (MTC). A hypothesis of C-cell dedifferentiation has been raised. Here, we evaluated the expression of CA19.9 and CD133, a stem cell marker, in MTC tissues. METHODS MTC samples from patients attending a university-based hospital were evaluated for CA19.9 and CD133 expression by immunohistochemistry. Clinical data were retrieved from medical records. RESULTS Tumor specimens from 70 MTC patients (57.1% hereditary) were evaluated. The age at diagnosis was 36.1 ± 16.3 years, and 58.6% were female; 53% of patients had cervical and 20% distant metastases. CA19.9 staining was detected in 87% of the samples, but no association was observed with biochemical markers, tumor size, local or distant metastases (All P > 0.05). Remarkable, CA19.9 expression was higher in the metastasis than in primary tumor samples (P = 0.0002). CD133 was expressed in 90.5% samples, but no correlation was found with CA19.9. Interestingly, we identified three distinct expression patterns to CA19.9: individual, focal, and diffuse cells. Sporadic MTC was associated with the individual cell pattern (70.6%), while the hereditary form with the focal expression pattern (63.9%; P = 0.04). Remarkably, the diffuse pattern was associated with larger tumor size and distant metastases (P = 0.032). CONCLUSIONS The majority of samples stained for CA19.9, suggesting it is an MTC cell-intrinsic feature. Three distinct expression patterns were identified, which were associated with the hereditary or sporadic form, larger tumor size, and presence of metastases.