ACTH-secreting medullary carcinoma of the thyroid: Monitoring of clinical course with calcitonin and cortisol assays and immunohistochemical studies

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Abstract
The clinical course of a patient with Cushing's syndrome secondary to metastatic medullary carcinoma of the thyroid was documented with serial calcitonin and cortisol assays and tumor immunohistochemistry studies. Cortisol levels were originally markedly elevated but returned to normal after total thyroidectomy. These levels rose again when the patient developed liver metastases but normalized during chemotherapy, never to rise again despite the appearance of cervical lymph node metastasis. Calcitonin levels remained elevated throughout the course. The original tumor was composed of two cell lines: one containing both calcitonin and ACTH and another containing only calcitonin-reacting cells. However, the cervical metastasis showed a marked decrease in both cell lines with fever than 1% of cells reacting to ACTH, and only 25% to calcitonin. The almost total disappearance of ACTH-reacting cells may have been therapeutically induced or may represent a consequence of tumor progression.