Thyroglobulin measurement in monitoring response to radioiodine treatment in children with differentiated thyroid carcinoma (DTC) and lung metastases

Abstract

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Objectives: Distant metastases, mainly to lung, are diagnosed in about 20% of children with DTC. Radioiodine (131-I) therapy is a treatment of choice in that case. Loss of radioiodine uptake, full radiological and biochemical recovery with thyroglobulin (Tg) serum level below cut-off level are expected to be documented to diagnose complete remission. The aim of the study was to evaluate Tg serum level response as a tool in follow-up of children with DTC and lung metastases treated by 131-I. Methods: From 235 children (age 4 to 18) diagnosed with DTC, 42 (17.9%) had lung metastases, in 40 cases 131-I-avid and only in 8 positive in radiological examinations. All were treated with 131-I (accumulated activities 100 to 950 mCi). To assess lung uptake and response, post-therapy WBS (95%) or diagnostic WBS (5%) was performed. Tg was evaluated either during TSH stimulation (cut-off at 10 ng/ml) or during T4 therapy causing TSH suppression (cut-off at 1 ng/ml). Tg results in patients with recovery (Tg rec) <70% were not studied. Results: Tg rec was <70% in 3 children (8%), so Tg results from 36 children were studied. The median Tg value at the diagnosis of metastases, measured at T4 withdrawal, was 175 ng/ml (in all but one > 10 ng/ml) and was significantly higher than in the group without lung dissemination (median 3.5 ng/ml). In children with 131-I avid metastases, after treatment, scintigraphic CR was achieved in all cases and radiological in 7 out of 8. After 131-I treatment, Tg serum level was decreasing in all children, however, it normalized at the last radioiodine treatment only in 13 (36%). During the follow-up Tg continued to decrease and the last stimulated Tg was below 10 ng/ml in 23 (64%) patients. The median time of follow-up was 75 months and did not differ between children with normal and elevated Tg concentration. Conclusions: Biochemical CR can be achieved in about 2/3 of children with DTC lung metastases but in most cases requires a long follow-up period. In a case of complete scintigraphic remission and decreasing Tg serum concentration careful follow-up but not further radioiodine therapy is indicated.