Recurrence-free survival and prognosis after adjuvant therapy with radioactive iodine-131 in patients with differentiated thyroid carcinoma.

This study aimed to assess recurrence-free survival (RFS) rates and recurrence-related factors of patients who received adjuvant therapy (AT) with radioactive iodine (RAI) for differentiated thyroid cancer (DTC) following thyroidectomy. We evaluated 284 patients who underwent AT between January 2011 and July 2020 at our hospital. Recurrence was defined as visible recurrent lesions on image analysis or need for repeat surgery with pathologically confirmed recurrent lesions. RFS rate and prognostic factors were statistically evaluated. The median observation period was 30.2 months (range, 5.7-294 months). Overall, 192 patients were female and 92 were male, and the median age was 54 years (range, 9-85 years). Initial assessment revealed 39 recurrence cases. The 3-year RFS rate was 85.8% (95% confidence interval: 81.1-90.9%). Univariate analysis revealed that histology (except for papillary carcinoma), Tg level > 4 ng/dL before AT, and AT result significantly exacerbated the RFS rate. In multivariate analysis, histology and AT result were also important contributors to the worsening RFS rate. Results of AT can be determined relatively early and are important in predicting future recurrence in patients with DTC. Increasing the success rate of AT may lead to an improved prognosis.

Comparison of thyroid hormone withdrawal and recombinant human thyroid-stimulating hormone administration for adjuvant therapy in patients with intermediate- to high-risk differentiated thyroid cancer.

OBJECTIVE: To compare the clinical outcome in patients who received adjuvant therapy with radioactive iodine (RAI) using different preparation methods, namely, thyroid hormone withdrawal (THW) and recombinant human thyroid-stimulating hormone (rhTSH), after undergoing thyroidectomy for intermediate- to high-risk differentiated thyroid carcinoma (DTC) according to the American Thyroid Association criteria. METHODS: Between May 2012 and October 2018, 136 patients who underwent adjuvant therapy with high-dose (3700 MBq) RAI for DTC without any metastatic lesions or macroscopic residual lesions after surgical resection were retrospectively selected. Patients were excluded if distant metastasis was confirmed during adjuvant therapy or if the outcome could not be confirmed; thus, 112 patients were finally evaluated. Patients underwent either a 3-week I restriction with thyroxine withdrawal or a 2-week I restriction with rhTSH administration. The serum thyroglobulin (Tg) concentration was measured, and 131I scintigraphy (370 MBq) was performed 6-12 months after adjuvant therapy. The definition of the initial achievement of adjuvant therapy was the disappearance of the uptake of 131I at the thyroid bed and serum Tg concentration < 2.0 ng/mL. The results of the adjuvant therapy between the groups were compared using the Fisher's exact test, and the TSH levels and estimated glomerular filtration rate (eGFR) were compared using the Welch's t test. RESULTS: The THW and rhTSH groups included 47 and 65 patients, respectively, and the intermediate- and high-risk groups included 63 and 49 patients, respectively. No patient was assigned to the low-risk group. In the THW and rhTSH groups, the initial RAI adjuvant therapy goal was achieved in 30/47 (63.8%) and 46/65 patients (70.8%), respectively (p = 0.54); mean ± standard deviation of the TSH levels was 123.8 ± 46.4 µIU/mL and 274.5 ± 97.7 µIU/mL, respectively (p < 0.01), and eGFR (treatment/pre-treatment) was 0.81 and 0.99, respectively (p < 0.01). In the intermediate- and high-risk groups, the initial RAI adjuvant therapy goal was achieved in 43/63 patients (68.3%) and 33/49 (67.3%), respectively (p = 1.0). CONCLUSION: No significant differences were observed between the preparation methods in the initial achievement of RAI adjuvant therapy. However, patients in the rhTSH group demonstrated higher TSH levels and retained eGFR.

Comparison between the different doses of radioactive iodine ablation prescribed in patients with intermediate-to-high-risk differentiated thyroid cancer.

OBJECTIVE: This study aimed to compare the clinical outcomes of patients who received radioactive iodine (RAI) ablation after undergoing thyroidectomy for intermediate-to-high-risk differentiated thyroid carcinoma (DTC) according to the American Thyroid Association (ATA) criteria. METHODS: We retrospectively examined patients who underwent RAI ablation for DTC after surgical resection without macroscopic residual lesions or metastatic lesions between December 2011 and August 2016. Among 147 patients who underwent RAI ablation, those whose initial pathological stages or RAI ablation results were unknown and whose distant metastases were confirmed during RAI ablation were excluded. Low-dose therapy was defined as administration of 1110 MBq of 131iodine (131I), while high-dose therapy referred to administration of 2960-3700 MBq of 131I. We defined initial success of RAI ablation as a serum thyroglobulin concentration of < 2.0 ng/mL without thyroid-stimulating hormone stimulation and disappearance of 131I uptake in the thyroid bed on 131I scintigraphy 6-12 months after RAI ablation. RAI ablation success rates were compared between the low-dose and high-dose groups using Fisher's exact test, and inverse probability of treatment weighting (IPTW) analysis was performed for adjusting potential biases. RESULTS: Among the 119 patients examined in this study (39 men and 80 women), 79 were classified as having intermediate risk, while 40 were classified as having high risk based on the ATA guideline. Initial RAI ablation success was achieved in 50/68 (73.5%) patients from the low-dose group and in 36/51 patients (70.6%) from the high-dose group (p = 0.84). Moreover, IPTW analysis showed no significant difference between the low-dose and high-dose groups. However, the success rate tended to be superior in high-risk patients who received high-dose therapy (86.2%) than in those who received low-dose therapy (72.7%) (p = 0.37). CONCLUSION: There was no significant difference in the RAI ablation success rate between the low-dose and high-dose groups involving patients with intermediate-to-high-risk DTC. However, high-dose RAI ablation may be recommended in high-risk patients.