Medullary Carcinoma of the Thyroid Gland

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Abstract
In two patients with medullary carcinoma of the thyroid gland tumor extracts contained 1000 to 2000 times more hypocalcemic activity than normal human thyroid tissue. Activity was detected by bioassay in plasma of both patients. One had severe hypocalcemia and hypophosphatemia. Hypocalcemic activity rose in response to calcium infusion and closely paralleled changes in plasma calcium. Several lines of evidence supported the conclusion that the hypocalcemic material in tumors and plasma was thyrocalcitonin. Parallel log dose-response lines were obtained in bioassays of tumor extracts, plasma and porcine thyrocalcitonin. The hypocalcemic activity was lost during incubation with purified thyrocalcitonin-inactivating factor and hydrogen peroxide. Like authentic thyrocalcitonin, the activity did not sediment in the ultracentrifuge. Net synthesis of thyrocalcitonin was shown by culture of tumor cells in vitro. Human tumor thyrocalcitonin did not cross-react significantly in the radioimmunoassay for porcine thyrocalcitonin.