Should ‘low‐risk’ thyroid cancer patients with residual thyroglobulin be re‐treated with iodine 131?

Summary Objective  The American consensus statement on patients with low‐risk thyroid cancer, published in 2003, suggests repeat 131 I therapy if the thyroglobulin value is elevated at first follow‐up. We evaluated this strategy in our practice. Methods  Among 407 patients with thyroid cancer who had total thyroidectomy and 131 I ablation between January 2000 and December 2003, 12 patients with stage I thyroid cancer (any tumour (T), any node (N), metastasis (M)0 if < 45 years or T1, N0, M0 if > 45 years), were re‐treated on the basis of their thyroglobulin level at first follow‐up. Mean patient age was 32·8 years. None of them had a T4 tumour. Thyroglobulin levels after thyroid hormone withdrawal ‘off‐T4’ ranged between 4·5 and 251 ng/ml (median 8). One to four courses of 3·7 GBq 131 I were given. Results  Three patients had a negative 131 I therapy scan and an uneventful course. Two patients had slight residual uptake only in the thyroid bed and negative ultrasound examination. Four patients had isolated 131 I uptake in the mediastinal region. No abnormalities were found on complementary mediastinal imaging. This finding was interpreted as benign 131 I thymic uptake. The last three patients also had mediastinal thymic uptake associated with a slight thyroid bed uptake. One patient had a gradual increase in the thyroglobulin level, and underwent resection of nonfunctioning neck lymph nodes. Thyroglobulin levels declined in all other patients. Conclusions  No distant lesions were found in a group of young ‘low‐risk’ thyroid cancer patients given empirical 131 I therapy for residual thyroglobulin. When blind 131 I therapy shows no uptake, or uptake limited to the thymus, 131 I therapy should not be repeated. The authors also briefly discuss the hypothesis that enhanced thymus might be a source of benign thyroglobulin secretion.