Radioactive iodine treatment in medullary thyroid carcinoma

Background Elevated levels of basal and stimulated calcitonin are commonly seen in hereditary and sporadic medullary thyroid cancer (MTC) following total thyroidectomy. The cause of these high levels can be residual thyroid tissue, possibly with C-cell hyperplasia, and/or residual micro-MTC foci. MTC does not have the ability to concentrate radioactive iodine. However, radioactive iodine trapped by thyroid follicular cells may affect the neighbouring parafollicular cells. Aim To investigate the effect of radioactive iodine treatment as adjuvant therapy to surgery in seven patients with persistent elevation of basal and stimulated calcitonin levels. Methods Pentagastrin testing was performed in each case immediately before surgery and at intervals of 6 months over a maximum period of 5 years (range, 44-60 months) after surgery. Results A significant decrease in basal and stimulated calcitonin levels was observed in three patients whose disease was localized to the thyroid gland at the final visit. In the remaining four patients, who initially had lymph node involvement at surgery, basal and stimulated calcitonin levels were decreased significantly in only one. At follow-up, of the three patients who showed no decrease in basal and stimulated calcitonin levels, two developed further regional lymph node and distant metastases. Conclusions In patients with persistently elevated basal and stimulated calcitonin levels, radioactive iodine treatment may be the therapy of choice for C-cell hyperplasia and/or micro-MTC after optimal thyroid surgery, especially if the disease has not spread beyond the thyroid gland.