Low postoperative nonstimulated thyroglobulin as a criterion for the indication of low radioiodine activity in patients with papillary thyroid cancer of intermediate risk ‘with higher risk features’

Summary Objective This study evaluated low‐activity 131 I therapy in patients with papillary thyroid carcinoma ( PTC ) of intermediate risk ‘with higher risk features’ who had low nonstimulated thyroglobulin (Tg) after thyroidectomy. Design and Patients This was a prospective study including 102 patients with tumours >1 cm and aggressive histology; and/or >3 positive lymph node ( LN ) or LN >1·5 cm or exhibiting macroscopic extracapsular extension, and clinically apparent ( cN 1); and/or a combination of a tumour >4 cm, microscopic extrathyroidal extension and LN metastases ( cN 1). After thyroidectomy, all patients had nonstimulated Tg < 0·3 ng/ml and negative antithyroglobulin antibodies (TgAb) and neck ultrasonography ( US ). The patients were treated with a low activity of 131 I (1110 or 1850 MB q). Results Post‐therapy whole‐body scanning (Rx WBS ) showed ectopic uptake in four patients. When evaluated 12 months after 131 I therapy, nonstimulated Tg ≤ 0·2 ng/ml with negative TgAb and US , defined as excellent response to initial therapy, was achieved in 101 patients (99%). Only one patient with positive initial Rx WBS had structural disease. During follow‐up, four patients (4%) relapsed, including LN metastases in two, pulmonary metastases in one, and elevated Tg in one. The other 98 patients remained with nonstimulated Tg ≤ 0·2 ng/ml and negative TgAb and US . There was no case of death due to the tumour. Conclusions We conclude that in intermediate‐risk patients ‘with higher risk features’, low nonstimulated Tg measured with a second‐generation assay can be used as criterion for the administration of low 131 I activities (1850 MB q or less).