Efficacy of adjuvant therapy with 3.7 GBq radioactive iodine in intermediate-risk patients with ‘higher risk features’ and predictive value of postoperative nonstimulated thyroglobulin

AIM: This study evaluated the efficacy of adjuvant therapy with 3.7 GBq radioactive iodine (RAI) in patients with papillary thyroid carcinoma (PTC) of intermediate risk with higher risk features and determined the predictive value of postoperative nonstimulated thyroglobulin (Tg). METHODS: This was a prospective study including 85 patients with PTC of intermediate risk and higher risk features: tumor greater than 1 cm and aggressive histological subtype or vascular invasion; and/or more than three positive lymph node (LN) or LN greater than 1.5 cm or showing macroscopic extracapsular extension; and/or a combination of tumor greater than 4 cm, microscopic extrathyroidal extension, aggressive histology, and LN metastases (cN1). After thyroidectomy, all patients had nonstimulated Tg of at least 0.3 ng/ml and ultrasonography showed no anomalies. RESULTS: When evaluated 12 months after RAI therapy, an excellent response to initial therapy was achieved in 61 patients (71.7%). Structural disease was detected in five patients (5.9%). During follow-up, 6/80 patients (7.5%) without structural disease 1 year after RAI developed relapse. In the last assessment, 80 patients (94.1%) had nonstimulated Tg less than 1 ng/ml and no evidence of structural disease. There was no case of death because of the tumor. Postoperative nonstimulated Tg was a predictive factor of the main outcome (structural disease 1 year after RAI or recurrence) and the best cut-off was 1.8 ng/ml (sensitivity: 72.7%, specificity: 83.4%, negative predictive value: 95.4%). CONCLUSION: In patients with PTC of intermediate risk with higher risk features treated with 3.7 GBq RAI, postoperative nonstimulated Tg up to 1.8 ng/ml was a predictor of low risk of structural disease 1 year after therapy or recurrence.