Role of calcitonin (Ct) in wash-out fluid from fine-needle aspiration (FNAB) in the diagnosis of medullary thyroid cancer (MTC): comparison with basal calcitonin, cytology and pentagastrin stimulation test (Pg-Test)
Vincenzo Rochira, Chiara Diazzi, Lucia Zirilli, Stefania Romano, Cesare Carani & Bruno Madeo
Introduction: Serum Ct is considered the most sensitive tool for MTC screening, but with poor specificity. Pg-test sensitivity and specificity are high, but doubtful for 30100 pg/ml of Ct peak. FNAB is not routinely used due to its very low sensitivity and specificity. Only few studies from a small number of patients are available on the role of Ct measurement in the wash-out fluid (Ct-FNAB) for MTC diagnosis, providing conflicting results.
Aim of the study: To assess clinical usefulness of Ct-FNAB in the identification of primary MTC in thyroid nodules.
Subjects and methods: Thirty-three patients (10M, 23F, mean+S.D. age: 55.5+11 years), with thyroid nodules and concomitant increased basal serum Ct. All subjects underwent a Pg-stimulated Ct evaluation and a total of 54 thyroid nodules underwent US-guided FNAB for both cytology and Ct-FNAB.
Results: Ct-FNAB levels in nodules with MTC or C-Cells Hyperplasia (CCH) was significantly (P<0.0001) higher than in hyperplastic nodules and than serum Ct (P=0.02). The sensitivity and the specificity for basal Ct were 100 and 18.2% respectively. The sensitivity for Pg-test resulted 100%, and the specificity 95.4%. Cytology sensitivity was very low (10%) with a specificity of 95.4%. The ROC curves showed that both Ct-FNAB and Pg-test to correctly distinguish MTC or CCH nodules from hyperplastic nodules better than basal Ct. Regarding Ct-FNAB alone the best pair of values for highest sensitivity (90%) and specificity (100%) was found using a cut-off of 100 pg/ml or of 36 pg/ml, with the best values at 100 pg/ml.
Discussion: The results of this study suggest that using both the cut-offs of 36 and 100 pg/ml, Ct-FNAB may be an highly reliable marker with a high sensitivity and specificity for MTC early detection in skilled hands. In clinical practice, only Ct-FNAB allows to know the exact localization and size of MTC already before thyroidectomy.