Procalcitonin Measured By Three Different Assays Is An Excellent Tumor Marker For The Follow-Up Of Patients With Medullary Thyroid Carcinoma

Objectives: Procalcitonin (PCT) has been suggested as a tumor marker in patients with medullary thyroid carcinoma (MTC). Clinical application data in long term followup are missing.Methods: 210 serum samples of 169 consecutive patients with MTC (92 sporadic, 77 hereditary, 158 postoperative follow-up, 11 preoperative) were collected between 2018 and 2020. Postoperative patients were stratified into three groups according to their disease status at the end of follow-up: cured (n=51, calcitonin (CT) levels < limit of quantitation), minimal residual disease (n=55, detectable CT and no metastases provable by imaging methods), metastatic disease (n=52). In five patients CT and PCT were measured while on therapy with tyrosine kinase inhibitors (TKI). CT was analyzed by the Roche ECLIA, PCT by three assays from Roche, PES, Abbott.Results: The mean +/- SD values seen with the three PCT assays in the MTC response groups, cured: <0.06, 0.016 +/- 0.007, 0.014 +/- 0.007 ng/mL, minimal residual disease: 0.511 +/- 0.800, 0.389 +/- 0.687, 0.341 +/- 0.614 ng/mL, metastatic disease 109 +/- 202, 60.4 +/- 110, 63.3 +/- 115 ng/mL correlate well with the CT results in these groups: cured <1.0 pg/mL, minimal residual disease 91.3 +/- 121.5 pg/mL, metastatic disease 14,489 +/- 30,772 pg/mL. There was a significant correlation (p<0.001) between the three PCT assays (Roche/PES r=0.970, Roche/Abbott r=0.976, Abbott/PES r=0.995). In the course of treatment with TKI both CT and PCT reflected clinical state. Preoperative PCT in hereditary MTC has the same diagnostic validity than CT.Conclusions: PCT measured with three different immunoassays is as good as the standard tumor marker CT in the follow-up of MTC but has a superior analytical stability.