Heterogeneity of immunoreactive calcitonin in extracts of medullary thyroid carcinoma

Tumor extracts from 9 patients with medullary thyroid carcinoma were studied to determine if multiple forms of immunoreactive calcitonin existed within the tumors. Calcitonin was extracted from the tumors with 0.1 N formic acid and the extracts were evaluated by gel filtration on columns of Bio-Gel P-10 and radioimmunoassay of the fractions obtained. Serum calcitonin concentrations were high enough in 3 patients to allow for similar evaluation. Four immunoreactive peaks of calcitonin were found after chromatography of the tumor extracts. Three of the peaks eluted earlier than monomer human calcitonin. 6 tumor extracts contained all four immunoreactive peaks while 3 had only two. In 2 patients four immunoreactive peaks of calcitonin were found in both the serum and the tumor extracts while 1 patient had three peaks in the serum but only two peaks were detected in the tumor extract.