The case records of 235 patients who were treated for differentiated thyroid cancer between 1949 and 1981 were reviewed. Forty-two (18%) had distant metastatic spread outside the neck and received radioiodine (131I) therapy. In cases where the distant spread was confined to the lungs, 54% of patients were alive, free of disease, 10 years after 131I treatment was started. By contrast, no patient with skeletal involvement has survived for 10 years and only one for five years after treatment. A variety of cytotoxic drugs has been tried on an ad hoc basis with no notable success. One patient developed preleukaemia three months after completion of 131I treatment, but no other serious side effects were observed. Factors that influence the behaviour of metastatic thyroid carcinoma are discussed and a possible revised approach to 131I therapy is suggested in the light of these findings.
Well differentiated thyroid cancer is a rare disease in the UK. It is the only cancer which, having metastasized, remains curable by radioisotope therapy with 131I. The main indication for administering repeat doses of 131I is the appearance of abnormal uptake in a whole body scan following diagnostic or therapeutic 131I administration. False positive scans, showing the presence of 131I uptake in the absence of residual thyroid tissue or metastases can occur, although they are uncommon. Unless recognized as a false positive, 131I uptake may result in diagnostic error and lead to administration of an unnecessary therapy dose. We describe a series of nine patients in whom the scans showed false positive uptake of 131I, including cases where the cause of the uptake is still uncertain. We demonstrate the common sites of false positive uptake, discuss the underlying mechanisms and suggest a systematic approach to the interpretation of whole body scans in order to prevent unnecessary treatment with 131I.
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