Medullary thyroid carcinoma (MTC) should be considered in the differential diagnosis of patients with unexplained persistently high carcinoembryonic antigen (CEA), with or without elevated calcitonin levels, as illustrated in a recently published study in Cureus.

Calcitonin is considered a diagnostic marker for MTC, with a sensitivity of approximately 98%. Although considered rare, several reports of patients with MTC and normal serum calcitonin levels exist, the researchers noted. MTCs without elevated calcitonin levels account for up to 5% of all cases, they added.

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“While elevated calcitonin levels are a useful diagnostic biomarker for medullary thyroid carcinoma (MTC), some patients with poorly differentiated MTC or metastasis may not have elevated levels of calcitonin,” the authors wrote.

The case involved an 81-year-old female with a history of IA hormone receptor positive, human epidermal growth factor receptor-2, referred due to persistently elevated CEA levels during the last 15 years. Further questioning revealed weight loss, fatigue, and joint pain during the last 2 years.

CEA is a nonspecific marker associated with MTC and several other tumor types.

Physical examination was unremarkable, and laboratory work-up did not reveal other breast-cancer-associated tumoral markers apart from CEA. CEA levels had progressively risen since 2010 until 2021. The patient underwent a full-body MTC scan that showed no relevant findings. A subsequent PET scan revealed decreased uptake at the right thyroid lobe, and ultrasound revealed several thyroid nodules without associated lymphadenopathies.

A fine needle aspiration biopsy showed results consistent with MTC; calcitonin levels and other thyroid function tests were within normal limits. The patient underwent a radical thyroidectomy which confirmed the diagnosis. After the surgery, CEA levels dropped progressively.

“In summary, this case highlights the significance of monitoring serum CEA levels as a diagnostic biomarker for MTC, especially in cases where serum calcitonin is negative,” the authors concluded.


Ukrani J, Barnes M, Ashraf A, Haggerty G, Dacosta N. Uncovering the uncommon: An 81-year-old woman with elevated carcinoembryonic antigen (CEA) but normal calcitonin levels diagnosed with medullary thyroid carcinoma. Cureus. Published online June 12, 2023. doi:10.7759/cureus.40290