MON-457 Reactive Thyroid C-Cell Hyperplasia or Medullary Thyroid Cancer in a Patient with Nodular Thyroidopathy. May the Calcitonin Measurement in Fine-Needle Aspirate Washout Fluid of the Healthy Lobe Help to Define These Conditions?

Background: Serum basal calcitonin (bCT) is used as a biomarker of medullary thyroid carcinoma (MTC) but bCT can also be elevated in patients with hypercalcemias, hypergastrinemias, thyroiditis, neuroendocrine tumors, renal end-stage kidney disease, obesity and cigarette smoking. The application of bCT and calcitonin measured in the FNA washout fluid sample (FNA-CT) for screening certain patients with nodular thyroidopathy can be controversial. Case: A 44 yo patient presented with elevated bCT level - 24pg/ml (N for male <18). He had a morbid obesity (BMI-45kg/m2) and thereby received GLP-1 receptor agonists Liraglutide 18 mg in total throughout one month. The ultrasound thyroid examination showed 2 nodules in the right lobe: 11mm and 9 mm (EU-TIRADS 2 and 4). Thyroid nodules were evaluated by fine needle aspiration biopsy (FNAB) which revealed benign colloid nodules (Bethesda II). Following the most updated ATA guidelines, to accurately diagnose MTC we performed FNA-CT measurement. The concentration from both nodules exceeded the upper reporting range of 2000 pg/ml. The patient stopped his therapy with Liraglutide and after one month of following, his bCT dropped at 18 pg/ml. He underwent a second workup with same results. We examined FNA-CT of contralateral healthy lobe and obtained 913 pg/ml. After this case, 17 patients with high-normal rate of bCT: 14 of them had a nodule (Bethesda II) and elevated FNA-CT of healthy tissue of the contralateral lobe (>2000 pg/ml) were determined in follow-up group. The remaining 3 patients with nodules (Bethesda IV-VI) and FNA-CT of healthy lobe which did not exceed bCT rate, were operated. MTC was confirmed. Discussion: Our patient had not only many factors which can occur his bCT level (obesity, smoking), but also unfavourable FNA washout results. Additionally, since in clinical studies GLP-1 receptor activation has been associated with C-cell hyperplasia (CCH), we cannot completely exclude the possible effect of this treatment on patient’s bCT level. We confronted a situation when, on the one hand, FNA-CT data indicate the MTC nature of hypercalcitoninemia, but on the other hand, decreasing bCT-level in dynamic observation is not common for MTC. FNAB of the healthy lobe and obtaining high rates of CT in the washout fluid sample allowed us to confirm the diffuse CCH process, thus to follow up these patients. CT stimulation test cannot distinguish between minimal MTC and CCH and has no reference range. The weak point of the proposed study is the lack of morphological data in the follow-up group of patients. Conclusion: It is possible to use rate of FNA-CT of the healthy lobe to differentiate between various C-cell diseases, but requires new data.