THE FUNCTION OF VARIOUS TYPES OF THYROID CARCINOMA AS REVEALED BY THE RADIOAUTOGRAPHIC DEMONSTRATION OF RADIOACTIVE IODINE (I131)*†

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Abstract
100 consecutive cases of carcinoma of the thyroid from patients who had received "tracer" or "therapeutic" doses of radioactive I131 were studied by the radioautographic technique. 46 gave radioautographic evidence of concn. of the isotope in the carcinoma. The histologic pattern of the tumor appeared to have a significant association with the concn. of the isotope, in that types with abundant colloid were more likely to concentrate I131 than those types not containing colloid. The latter rarely concd. the isotope. Factors other than the presence of colloid must also be very significant, for some follicles showed no activity whereas morph. similar, neighboring follicles were heavily laden with I131. Positive radioautographs have been obtained showing concn. of I131 when the tissue concn., as measured over a sq. cm., has been less than 0.2 microcuries per g. of tissue. In no case have we seen a concn. of I131 in thyroid carcinoma tissue greater than, or equal to, the concn. in adjacent thyroid tissue. There were 32 cases in which a radioautograph contained both normal thyroid and carcinoma tissue; the former showed concn. of the isotope and the carcinoma gave no evidence of such concn. The uneven, variable concn. of I131 in normal as well as neoplastic thyroid tissue raises fundamental questions, such as the possible phasic function of the thyroid follicle. It also emphasizes the problem of the calculation of therapeutic doses.