SAT560 A Case of Medullary Thyroid Carcinoma with Increasing Carcinoembryonic Antigen and Stable Calcitonin Levels

Disclosure: K.N. Youssef: None. L. Salej: None. A. Gavrila-Filip: None. Background: Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from the parafollicular or C cells of the thyroid gland that secretes different tumor markers, including calcitonin (CT) and carcinoembryonic antigen (CEA). CT is only produced by parafollicular cells, while CEA is a non-specific marker produced in various normal tissues, such as epithelial cells of the gastrointestinal tract, lung, breast, and prostate. Different benign and malignant conditions are associated with elevated serum CEA levels. Clinical case: A 69 years-old active smoker male with a history of nasal squamous cell carcinoma (SCC) status post resection in the remote past and bilateral pulmonary nodules underwent total thyroidectomy for a thyroid nodule with FNA positive for medullary carcinoma. Surgical pathology revealed a unifocal 1.5 cm medullary carcinoma with clean surgical margins and no lymphadenopathy. Pre-operative studies included an elevated serum CT of 388 pg/mL (normal ≤ 10 pg/mL), normal serum calcium and PTH levels and a normal 24-hour urinary test for pheochromocytoma. Family history was irrelevant, and the RET proto-oncogene test was negative. Initial post-operative serum CT levels were undetectable and CEA levels were normal (0-4 ng/mL). CT levels increased slowly over the next five years and then they remained stable in the range of 32 to 45 pg/mL. Serum CEA started to rise progressively 7 years after the thyroid surgery up to 6.5 pg/mL. Follow-up neck ultrasounds showed no local recurrence or lymphadenopathy. An extensive evaluation was performed to search for possible MTC metastases and other etiologies for the elevated CEA levels. Bone scan was negative. Chest CT scans revealed enlarging small bilateral pulmonary nodules; stable calcified mediastinal lymph nodes were noted, consistent with chronic granulomatous disease. PET-CT scan showed pulmonary nodules, too small to characterize. The patient underwent a left lower pulmonary lobe robotic-assisted wedge resection. Surgical pathology revealed keratinizing SCC, though to represent primary lung SCC versus metastases from his prior nasal SCC. Upper endoscopy and colonoscopy with biopsy were negative for malignancy. On further workup, the patient was diagnosed with prostate adenocarcinoma and underwent surgery followed by external beam radiation with hormonal therapy. Serum CEA levels normalized one year after the prostate cancer treatment. Serum CT levels remained stable. Conclusion: In patients with MTC who show increasing serum CEA and stable CT levels during follow-up after the initial treatment, it is important to exclude other etiologies before concluding that this change is related to a progression of the medullary cancer. Reference: Carcinoembryonic Antigen. Kankanala VL, Mukkamalla SKR.2022 Jan 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Presentation Date: Saturday, June 17, 2023