Discordance between Plasma Calcitonin and Tumor-Cell Mass in Medullary Thyroid Carcinoma

MEDULLARY thyroid carcinomas always secrete calcitonin, leading to an increased plasma hormone concentration.¹ The plasma calcitonin concentration usually correlates with the clinical extent of disease.² This article describes a patient with medullary thyroid carcinoma in whom plasma calcitonin did not correlate with estimated tumor burden. Although the tumor had metastasized widely, plasma calcitonin concentration was unexpectedly low. Immunohistochemical analysis of tumor tissue provides an explanation for this observation and illustrates a potentially important feature of human tumor biology. Case Report A 46-year-old man underwent hemithyroidectomy after the discovery of a thyroid nodule, which proved to be a medullary thyroid carcinoma.