In the last ten years, 47 patients with distant
metastases of differentiated
thyroid carcinoma have been treated with 131I following total
thyroidectomy. Post-
therapy whole body 131I scans revealed detectable uptake in the metastatic lesions in 23 (62%) of 37 patients with lung
metastases, 10 (67%) of 15 patients with bone
metastases five (71%) of seven patients with mediastinal
metastases, and neither of two patients with
brain metastases. The concentration of 131I in the
metastases was significantly correlated with serum T3 and T4 concentrations, and inversely correlated with serum TSH concentrations. Most of the patients with a strong positive scan were euthyroid, suggesting that
thyroid hormones produced by the
tumor compensated for
hypothyroidism following total
thyroidectomy. There was no significant relationship between serum
thyroglobulin concentration during T4 replacement
therapy and 131I uptake or the efficacy of
therapy. Twenty patients with lung (54%), five with bone (33%), two with mediastinal (29%), and none with
brain metastases showed
tumor regression
after treatment. Significantly increased 131I uptake in lung
metastases, better therapeutic results and better prognosis were demonstrated in young patients. In conclusion, age, 131I whole body scanning and serum
thyroid hormone concentrations are considered to be useful in predicting the efficacy of 131I treatment for distant
metastases, especially in the lung.