Disparity between tissue and serum calcitonin and carcinoembryonic antigen in a patient with medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of parafollicular or C-cells of thyroid that comprises 5-10% of all thyroid cancers [1, 2]. The neoplastic cells secrete calcitonin, carcinoembryonic antigen (CEA), and chromogranin A. Typically, increased serum levels of these tumor markers permit them to be used for initial diagnosis and long-term disease status surveillance. This article reports a case of sporadic MTC (pT2N0M0) in a young patient with normal serum tumor markers. A 16-year-old woman presented with MTC without evidence for this to be a familial case due to the absence of germline mutations in the RET proto-oncogene and negative family history. Surprisingly, there were normal preoperative serum levels of calcitonin, CEA, and chromogranin A, despite the immunohistochemistry showing strong and diffuse positive staining for these markers. This disparity between serum levels and tumor expression of calcitonin and CEA in MTC is quite rare. The relevant features of this case are discussed in consideration of the published experiences. This case may represent an unique subgroup of MTC with abnormal secretory capacity that requires reliance upon radiological evaluation for evidence of recurrent or disseminated disease, without the diagnostic benefit of serum tumor markers.