Postoperativestimulated thyroglobulin levels is a goodpredictor of the success ofthe first I131 ablative therapyin patients with low-risk differentiated thyroid cancer

Purpose: To determine the potential of postoperative-stimulated serum thyroglobulin levels (pre-Tg) immediately prior to initial I-131 ablative therapy (IAT) for predicting successful ablation in patients with low-risk differentiated thyroid carcinoma (DTC).Materials and Methods: Patients with DTC (n=662) treated with total or near-total thyroidectomy followed by immediate IAT were studied. Patients with positive anti-Tg autoantibodies, who did not meet the low-risk criteria, or with a recent history of iodine contamination were excluded. Patients were divided into three groups based: Pre-Tg levels ≤2 µg/liter, 2-10 µg/liter, and ≥10 µg/liter, using a threshold of 1 µg/liter for thyroglobulin levels at the time of the first D-WBS (Post-Tg). Diagnostic whole-body scans (D-WBS) and post-Tg levels were used to identify clinical outcomes (successful ablation, equivocal, or persistent disease). Various factors including age, sex, pre-Tg, and histopathology were analyzed to predict ablation success rates.

Results: One hundred and fifty-eight patients fulfilled the inclusion criteria, with no drop-out, from December 2008 to April 2012. Successful ablation patients had significantly lower pre-Tg levels at the first IAT (P <0.001 vs. unsuccessful ablation). Pre-Tg was the only factor significantly related with ablation success rates. After the first D-WBS, of 32 patients with pre-Tg &#8804;2µg/liter, 28 (87.5%) showed successful ablation, one (3.1%) was regarded as “equivocal”; and three (9.4%) showed persistent disease. Of 126 patients with pre-Tg >2 µg /liter, successful ablation was observed in 59 cases (46.8%), 32 (25.4%) were regarded as “equivocal”; and persistent disease was observed in 35 (27.8%). Pre-Tg level were significantly correlated with the outcome of the initial IAT (three by three χ² test, χ²=33, df=4, P <0.001).Conclusion: Pre-Tg &#8804;2 µg/liter is a promising factor predictive of successful ablation by the first IAT in patients with low-risk DTC.Key Words: low-risk differentiated thyroid carcinoma; thyroglobulin; I-131; prediction; successful ablation