A 37-year-old woman presented with a neck mass that proved to be medullary thyroid carcinoma by histologic and immunoperoxidase examinations. Serum calcitonin values were greatly elevated (over 100,000 pgsol;ml). There were widespread metastases in bone and liver. As the peripheral lesions showed only slight response to chemotherapy and local radiation therapy, potential use of radioiodine was studied. The bone lesions showed uptake of both Tc-99m MDP and radioiodide (l-131). Metastatic lesions were similar to the primary tumor in terms of histology, presence of calcitonin, and absence of thyroglobulin. Hence, the patient had a medullary thyroid carcinoma that took up radioiodide in its metastases. Two large oral doses of radioiodide (over 100 mCi each) did not significantly alter the serum calcitonin values, although there was a slight response in the activity of bone lesions. The whole body turnover of radioiodide was rapid (Tfrac12; equals; 0.7 days). Upon oral administration of lithium carbonate, whole-body radioiodide turnover slowed slightly (Tfrac12; equals; 1 day). If this effect were reflected in greater tumor retention of radioiodide (slower release), then agents that block radioiodide egress might have a role to play in therapy.
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