Prognostic implication of thyroglobulin and quantified whole body scan after initial radioiodine therapy on early prediction of ablation and clinical response for the patients with differentiated thyroid cancer.

OBJECTIVE: To investigate predictors for successful ablation and disease-free status after high-dose radioiodine therapy in patients with differentiated thyroid cancer.

METHODS: We enrolled 173 consecutive patients with differentiated thyroid cancer between November 2001 and December 2004 retrospectively (female 145, 46 ± 12 years). All patients underwent total thyroidectomy and I-131 ablative therapy (IAT) (3.7-5.4 GBq). The success or failure of ablation was assessed 6-9 months after the IAT with reference to undetectable thyroglobulin (Tg) and negative I-131 whole body scan (WBS). Afterward, the decision for disease-free status was evaluated using Tg and WBS (follow-up period after 1st IAT 7-81 months, median 43 months, criteria of disease-free: less than 10 ng/ml TSH-stimulated Tg or less than 2 ng/ml TSH-unstimulated Tg and/or negative WBS). Clinical and tumoral factors such as sex, age, pathologic type, the size of tumor, quantified cervical uptake in WBS1, pattern in WBS1, ablative therapy dose, AJCC stage, lymph node (LN) stage, Tg just before IAT (Tg1), and ablation status were assessed using logistic regression analyses.

RESULTS: There were 93 successful ablations (54 %). Significant predictors for the ablation failure were Tg1 (OR = 8.42; 95 % CI = 2.76-25.69; p < 0.0001), LN metastasis (OR = 3.05; 95 % CI = 1.11-8.37; p = 0.031), and quantified cervical uptake in WBS1 (OR = 4.95; 95 % CI = 1.07-22.88; p = 0.041). One hundred fifty-five patients were determined as disease-free after follow-up. All the eighteen patients with persistent disease were identified as ablation failure after first IAT. Significant predictors for the disease-free status were Tg1 (OR = 0.98; 95 % CI = 0.97-0.99; p = 0.028), tumor size (OR = 0.53; 95 % CI = 0.28-0.96; p = 0.044), and quantified cervical uptake in WBS1 (OR = 0.87; 95 % CI = 0.76-0.98; p = 0.024).

CONCLUSIONS: The thyroglobulin and quantified cervical uptake in whole body scan are significant predictors for the successful ablation and disease-free status after follow-up.