Treatment of Carcinoma of the Thyroid with Special Reference to Use of Radioactive Iodine

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RADIOACTIVE iodine is most effective in the treatment of well differentiated thyroid cancers. Since the majority of differentiated cancers are amenable to surgical cure, radioactive iodine is rarely required in these cases. Unfortunately, it is of no value in the highly malignant cancers in which it is most needed. For these reasons, the usefulness of I131 is limited to the small group of carcinomas of low malignancy which have metastasized or extended beyond the scope of surgical removal.

Role of I131 in the Treatment of Carcinoma of the Thyroid

Few carcinomas of the thyroid concentrate much radioactive iodine until the normal thyroid has been removed or destroyed with I131. As long as the normal thyroid is functioning, its greater avidity for iodine precludes any significant concentration of I131 by the tumor tissue. However many differentiated tumors, which before the thyroid was removed took up little or no I131, concentrate it satisfactorily after abolition of the function of the normal thyroid. Slight concentrations of radioactive iodine may occur even in tumors which seem to be quite undifferentiated, but in our experience the only tumors which can be made to concentrate I131 in therapeutic quantities are those which are well enough differentiated to have histologically demonstrable colloid. Two such tumors have been encountered in a series of 105 histologically proved cancers of the thyroid seen at the Cleveland Clinic in the past 5 years and, in both cases, pulmonary and cervical metastases have disappeared in response to treatment with I131.

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