Immunoreactive Calcitonin in Pheochromocytomas 1

Abstract

Abstract

Immunoreactive calcitonin (iCT) was evaluated in serum and tumor extracts from four successive, normocalemic patients with sporadic pheochromocytoma to determine how commonly these tumors contain CT-like immunoreactivity. Levels of iCT were measured by a nonequilibrium radioimmunoassay sensitive to both the intact molecule and the 11-32 amino acid region of human CT. With this assay, iCT is detectable in 56% of normal fasting adults (n = 52). The normal mean was 42 pg/ml with a normal range (mean ± 3 SD) of undetectable to 80 pg/ml. Serial dilutions of serum from a patient with medullary carcinoma of the thyroid and of acetic acid extracts of the pheochromocytomas gave displacement curves indistinguishable from the human standard. Patient “A” had an elevated serum iCT level of 477 pg/ml. After surgery for the pheochromocytoma, his basal serum iCT was normal and there was no abnormal elevation in iCT after pentagastrin stimulation. CT-like immunoreactivity was present in each of the four tumor extracts (2500-8600 pg iCT/g wet wt) and absent from an omental lymph node removed from patient A. Hypercal-citoninemia in patients with sporadic pheochromocytoma may not represent a concurrent medullary carcinoma of the thyroid since the presence and secretion of CT-like immunoreactivity from pheochromocytomas may be more common than previously realized.