Calcitonin-like polypeptides without apparent biological activity in a patient with recurrent medullary thyroid...

A 51-year-old male with a recurrent medullary thyroid carcinoma (MTC) showed high serum levels of calcitonin (CT) and carcinoembryonic antigen (CEA) but with concomitant normocalcemia. The CT activities of the patient's serum in vivo (hypocalcemic activity in rats) and in vitro (cyclic AMP-increasing activity in cultured human mammary tumor, T47D) were much lower than those expected from the patient's CT level. High performance liquid chromatography (HPLC) with radioimmunoassay (RIA) detection gave a broad spectrum of molecular weights of CT-like polypeptides in the 3 kDa to 200 kDa range with separation from CEA, suggesting that the mechanism for CT production in MTC is an obscure one.