Should 'low-risk' thyroid cancer patients with residual thyroglobulin be re-treated with iodine 131?

Objective: The American consensus statement on patients with low-risk thyroid cancer, published in 2003, suggests repeat ¹³¹I 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 ¹³¹I 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 ¹³¹I were given. Results: Three patients had a negative ¹³¹I 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 ¹³¹I uptake in the mediastinal region. No abnormalities were found on complementary mediastinal imaging. This finding was interpreted as benign ¹³¹I 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 ¹³¹I therapy for residual thyroglobulin. When blind ¹³¹I therapy shows no uptake, or uptake limited to the thymus, ¹³¹I therapy should not be repeated. The authors also briefly discuss the hypothesis that enhanced thymus might be a source of benign thyroglobulin secretion.