Calcitonin

Calcitonin (CT) is a peptide hormone secreted by thyroid parafollicular cells (C cells). It can not only inhibit the release of bone calcium to reduce blood calcium, but also regulate calcium and phosphorus balance by suppressing the reabsorption of phosphorus. Medullary thyroid carcinoma (MTC) is a highly malignant neuroendocrine neoplasm (NEN) that will induce abnormal proliferation of C cells and excessive secretion of CT. Therefore, CT has become an essential specific indicator for diagnosing MTC in clinical practice, and it is not expressed in differentiated thyroid cancer, which makes it applicable in differential diagnosis. However, some scholars found the atypical MTC with CT negativity, which may be due to the defect of CT synthesis mechanism or the mutation in antibody binding sites. In addition, CT can be expressed in gastrointestinal carcinoid, and its expression level is positively correlated with tumor pathological staging, indicating that the carcinoid has the trend of divergent or multidirectional differentiation during development. Meanwhile, some research suggested that the up-regulation of CT may promote epithelial-mesenchymal transition (EMT) in prostate cancer.