Procalcitonin: A Marker for the Diagnosis and Follow-Up of Patients with Medullary Thyroid Carcinoma

CONTEXT: Calcitonin (CT) is the main medullary thyroid carcinoma (MTC) tumor marker. However, it has several limitations, including a concentration-dependent biphasic half-life, sensitivity to rapid in vitro degradation, and the presence of different isoforms/fragments. Procalcitonin (PCT), the prohormone of calcitonin, is free of these limitations but is currently used only as a sepsis marker. OBJECTIVES: The objective of the study was to determine whether PCT is suited as a MTC tumor marker by comparing the diagnostic performance of PCT with that of CT in MTC. DESIGN: PCT and CT were measured in a total of 835 subjects, including normal volunteers (n = 197) and patients with active-MTC (n = 91), cured-MTC (n = 42), neuroendocrine tumors (n = 225), mastocytosis (n = 48), follicular cell-derived thyroid carcinoma (cured = 120, persistent/recurrent = 55), and benign thyroid disease (n = 57). RESULTS: PCT levels were significantly higher in the active-MTC patients (mean 126.4 ng/ml) than the cured-MTC patients (mean <0.1 ng/ml). The overall concordance between the two markers was 95.7% (kappa = 0.81). Receiver-operating characteristic curve analysis showed no significant difference in diagnostic performance between CT and PCT. PCT's diagnostic sensitivity and specificity were 91 and 96%, respectively. The corresponding values for CT were 99 and 98%. Analyte stability studies showed that CT is very unstable in vitro with a decrease of 35-50% from the original value 24 h after the blood draw, whereas PCT levels did not significantly change during this time. CONCLUSIONS: A strong correlation was observed between PCT and CT levels in patients with MCT. Given PCT's greater analytical stability, we conclude that it represents a promising complementary MTC tumor marker.