Calcitonin gene-related peptide as a tumor marker for medullary thyroid carcinoma

We have established a radioimmunoassay method for calcitonin gene-related peptide (CGRP) to monitor changes in plasma CGRP levels in patients with medullary thyroid carcinoma (MTC). Preoperative plasma CGRP levels (normal level less than 12.7 pg/ml) were as high as 128 pg/ml to 2,010 pg/ml in all five patients with MTC. Ten of 17 postoperative patients with MTC were positive for CGRP. A provocation test was performed in 12 patients with MTC. Plasma CGRP changes roughly paralleled serum calcitonin levels. In particular, in three patients with poorly-differentiated MTC which progressed aggressively, plasma CGRP levels were increased to 1.4 to 2.0 times levels before the test, i.e., lower than the 2.8- to 23.3-fold increase in nine patients with the well-differentiated MTC. These results suggest that CGRP may be a humoral marker of medullary carcinoma and be related to degree of malignancy.