Brain metastasis from calcitonin-negative medullary thyroid carcinoma.

Introduction: Medullary thyroid cancer (MTC) is a primary neuroendocrine tumor derived from parafollicular cells or C-cells of the thyroid gland. It accounts for 1% to 10% of all thyroid cancers and is the second most aggressive thyroid cancer after undifferentiated thyroid carcinoma. Serum calcitonin and carcinoembryonic antigen (CEA) concentrations are widely used as biomarkers to facilitate diagnosis and follow-up.