Abstract and Introduction
Abstract
Objective: Two large randomized trials of patients with differentiated thyroid cancer (DTC) reported recently (HiLo and ESTIMABL1) found that the recurrence rate among patients who underwent 1.1 GBq radioactive iodine (RAI) ablation was not higher than that of patients who underwent 3.7 GBq radioactive iodine (RAI) ablation. However, no similar studies have been conducted in China. We aimed to report clinical outcomes in Chinese patients with low/intermediate risk of recurrence DTC after long-term follow-up, and evaluate the risk factors that influence the presence or absence of incomplete response at the final follow-up.
Design: A long-term follow-up of a Chinese randomized clinical trial (October 2014 and February 2021) was conducted.
Patients: A total of 506 DTC patients at low/intermediate risk of recurrence who were randomized into two groups to receive 1.1 (n = 251) or 3.7 GBq (n = 255) RAI ablation following thyroid hormone withdrawal were followed on levothyroxine treatment for a median of 4.5 years (range: 1.6–6.3).
Measurements: Suppressed serum thyroglobulin (Tg) and anti-thyroglobulin antibody (TgAb) levels were determined, and neck ultrasonography was performed.
Results: At the final follow-up, 499 (98.6%) patients showed an excellent response. The other seven patients (two patients underwent 1.1 GBq and five patients underwent 3.7 GBq RAI ablation, respectively) showed either structural incomplete response (lymph node metastasis, n = 1), biochemical incomplete response (increased serum Tg ≥ 1 ng/ml, or increased positive TgAb levels, n = 5), or indeterminate response (stable positive TgAb levels, n = 1). The risk of incomplete response at the final follow-up was significantly increased in patients with stimulated serum Tg ≥ 10 ng/ml at ablation (p = .003) and in patients with unsuccessful ablation (p = .008).
Conclusion: Our findings indicated that there was no difference in the long-term outcomes with RAI ablation using either 1.1 or 3.7 GBq in patients with low/intermediate risk of recurrence DTC, and 1.1 GBq RAI might be suitable for patients who are recommended for ablation.
Introduction
Thyroid cancer is the most common endocrine and head and neck tumor, and it has become one of the 10 major cancers that is prevalent in China.[1] In 2015, approximately 200,700 new cases were diagnosed, accounting for 5.11% of all cancer cases, and the crude incidence rate was 14.60/100,000.[2] The most common type of thyroid cancer is papillary thyroid carcinoma (>90%).[2] Approximately 7900 thyroid cancer-related deaths were reported in 2015, accounting for 0.34% of all cancer-related deaths.[2]
Radioactive iodine (RAI) is administered to patients with differentiated thyroid cancer (DTC) after total or near-total thyroidectomy for remnant ablation, adjuvant therapy, or therapy for persistent disease.[3–5] Between October 2014 and July 2018, we performed a randomized, single-center clinical trial that included patients with low/intermediate risk of recurrence DTC to investigate the efficacy of RAI remnant ablation either with low (1.1 GBq) or high activity (3.7 GBq) after preparation with thyroid hormone withdrawal (THW; part of this trial has already been reported).[6] At 6–8 months, thyroid ablation was considered successful in 412 (87%) of 474 patients, and it was similar between the two groups.[6] Similarly, two European randomized, multicenter clinical trials also found that 1.1 GBq RAI ablation was as effective as 3.7 GBq RAI remnant ablation for patients with thyroid cancer.[7,8] Thus, from a short-term perspective, low-activity RAI ablation might be the optimal approach for patients with low/intermediate risk of recurrence DTC because of the satisfactory ablation rate, reduced radiation exposure, and lower healthcare costs.[9] However, the long-term follow-up findings remain unclear.
In 2013, a large retrospective study (n = 970) compared the long-term (median follow-up of 5 years) recurrence risk between patients who received low-activity (≤3.0 GBq) and high-activity (>3.0 GBq) RAI ablation, and reported that decreasing the activity of RAI ablation was not associated with an increased risk of recurrence.[10] Recently, two randomized, multicenter clinical trials (ESTIMABL1[11] in France and HiLo[12] in the United Kingdom) with long-term follow-up (median follow-up of 5.4 and 6.5 years, respectively) showed that RAI ablation activities or preparation methods did not have an influence on the risk of recurrence. However, no similar studies have been conducted in China. Therefore, in the present study, we aimed to report clinical outcomes in Chinese patients with low/intermediate risk of recurrence DTC after a median follow-up of 4.5 years and evaluate the risk factors that influence the presence or absence of incomplete response at the final follow-up.