Postoperative Stimulated Thyroglobulin of Less Than 1 ng/mL as a Criterion to Spare Low-Risk Patients with Papillary Thyroid Cancer from Radioactive Iodine Ablation

Background: Stimulated thyroglobulin (Tg) <= 1 ng/mL after thyroidectomy (after L-thyroxine [L-T4] withdrawal or administration of recombinant human thyrotropin [rhTSH]) has been proposed as a criterion to spare patients with papillary thyroid cancer (PTC), who are at low risk of recurrence, from ablation with iodine-131 (131 I). The objective of this prospective study was to evaluate the recurrence rate using this approach. Methods: This prospective study included 136 patients with PTC who underwent total thyroidectomy with apparently complete tumor resection and who presented no signs of persistent disease after surgery. The patients were classified as low risk of recurrence (nonaggressive histology, T1b-3 N0 M0). All patients had stimulated Tg <= 1 ng/mL, negative anti-Tg antibodies (TgAb), and neck ultrasound (US) showing no anomalies similar to 16 weeks after thyroidectomy, and none of them were submitted to ablation with 131 I. The time of follow-up ranged from 12 to 72 months (median: 44 months). Results: Among the patients studied, 134 (98.5%) continued to have serum Tg concentrations of <1 ng/mL during therapy with L-T4 (Tg/T4) and had negative TgAb and neck US. Lymph node metastases were detected by neck US in one patient. An increase of TgAb was observed in another patient, but she has not developed apparent disease to date. There was only one case of recurrence even among the 60 patients with tumors >4 cm or minimal extrathyroid invasion (T3 N0 M0). Conclusions: Low-risk patients with PTC who have stimulated Tg <= 1 ng/mL after thyroidectomy do not require ablation with I-131.