Calcitonin-negative medullary thyroid carcinoma: the 'triple-negative' phenotype

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of the thyroid, typically associated with elevated serum calcitonin.
• Calcitonin-negative MTC is a rare variant, posing diagnostic challenges due to its unique biochemical profile.

Observation:

• A case of a 24-year-old woman with a neck swelling is presented.
• Ultrasound revealed a thyroid nodule; however, serum calcitonin levels were normal.
• Histopathology confirmed MTC morphology but lacked calcitonin expression via immunostaining and in situ hybridization.

Findings:

• A diagnosis of 'triple-negative' calcitonin-negative MTC was established.
• The patient underwent successful surgical treatment (thyroidectomy and lymph node dissection).
• The patient remains disease-free three years post-surgery.

Implications:

• Measuring serum calcitonin, pro-calcitonin, carcinoembryonic antigen, and calcitonin gene-related peptide is vital when MTC is suspected, especially for identifying calcitonin-negative variants.
• Post-treatment monitoring of these markers is essential for managing calcitonin-negative MTC.
• Accurate diagnosis and monitoring aid in prognostic stratification and treatment decisions for this rare thyroid cancer.