Can sporadic medullary thyroid carcinoma be biochemically predicted? Prospective analysis of 66 operated patients with elevated serum calcitonin levels.

Measuring serum calcitonin (CT) in patients with thyroid diseases allows preoperative diagnoses of sporadic medullary thyroid carcinoma (MTC) and C-cell hyperplasia (CCH). The aim of this prospective study was to distinguish biochemically between CCH and MTC. Basal CT (bCT) was determined in 7276 consecutive patients referred for thyroid disease. Patients with recurrent, persistent, or familial MTC were excluded. When bCT was > 10 pg/ml a pentagastrin-stimulated CT (sCT) assay was performed. Patients were routinely operated on when bCT > 30 pg/ml or sCT > 100 pg/ml or when other indications for surgery were present. An extensive search for CCH or microscopic MTC was conducted by immunochemistry. Pathologic findings were correlated with the bCT and sCT values. In this study 66 patients were included. No morphologic alterations of C-cells were observed in 5 patients; 16 patients presented with CCH and 45 with MTC. Statistical analysis revealed a correlation of sCT and overall bCT with tumor size and staging (p <0.001). Considering cutoff values for bCT of < or = 30 pg/ml and for sCT of < or = 200 pg/ml, the positive predictive value of the test to detect MTC was 100% and the negative predictive value 63%. No patients with MTC at stage 2 to 4 had bCT <30 pg/ml or sCT <200 pg/ml. A bCT value of < or = 30 pg/ml or sCT < or = 200 pg/ml (or both) is highly predictive of MTC, requiring total thyroidectomy with lymph node dissection. Values of bCT <30 pg/ml and sCT <200 pg/ml do not distinguish between CCH and MTC at stage 1. In this case total thyroidectomy at least is recommended, and the role of nodal dissection might be discussed.