Optimizing Diagnostic Accuracy of Fine Needle Aspiration Biopsy Calcitonin Measurements in Detecting Medullary Thyroid Carcinoma

Detailed Summary

Medullary thyroid carcinoma (MTC) is a tumor originating from parafollicular C cells of the thyroid. (1) Representing 1 to 7% of all thyroid carcinoma cases (2, 3, 4). It can occur in two clinical forms, the sporadic or non-hereditary, in 75-80% of patients, and the hereditary form in the remaining 20-25%. It can be part of different clinical syndromes depending on the organs involved: Multiple Endocrine Neoplasia type 2A (MEN2A), Multiple Endocrine Neoplasia type 2B (MEN2B) and Familial Medullary Thyroid Carcinoma (FCM) whose clinical expression is only CMT. A distinctive characteristic of this tumor is its capacity to secrete calcitonin (CT), which, measured in serum, sanctions suspicion of this pathology (5-8) leading to diagnostic studies to confirm CMT. For the preoperative diagnosis of thyroid nodules, ultrasound-guided fine-needle aspiration cytology (FNAC) is a useful and safe procedure; however, its sensitivity to exclude CMT is low (9-15). In 2015, a meta-analysis of 15 studies (16) found that the accuracy of FNAC in diagnosing CMT was around 50%. For this reason, other studies have indicated that the measurement of calcitonin in the fine-needle lavage aspirate fluid of thyroid nodules (CT-guided FNAC), which have suspected medullary carcinoma, can significantly improve the accuracy in the diagnosis of MTC (17 -19). Therefore, clinical practice guidelines recommend its determination in patients with suspected MTC (1,2). The diagnostic importance of pre-surgical medullary carcinoma lies mainly in two points: first, it changes the surgical approach of the patients, and second, it allows one to rule out associated pathologies such as hyperparathyroidism and pheochromocytoma, which are associated when the entity is hereditary. The performance of CT-guided FNAC by the chemiluminescent (CL) method has been widely disseminated. However, to the best of our knowledge, to date there are no data available on the appropriate cut-off value of CT-guided FNAC with calcitonin electrochemiluminescence (ECL) immunometric assay method. As previously stated, it is of particular interest to determine the calcitonin cut-off point in needle washing by electrochemiluminescence method that allows diagnosing medullary carcinoma. Clarifying this point allows improving the approach to patients in whom medullary carcinoma is suspected. This work seeks to determine the cut-off point of CT-guided FNAC for the diagnosis of CMT with the ECL assay method.

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