Background: In the recent American Thyroid Association (ATA) guideline for adult differentiated thyroid carcinoma (DTC) patients, risk stratification is clearly defined and lobectomy is acceptable for low-risk DTC. However, risk stratification for children with DTC in the ATA pediatric guidelines is rather unclear, and total thyroidectomy is recommended for all patients with any risk. The aim of this study was to attempt risk stratification based on our experience and to consider the appropriate extent of thyroidectomy, especially for low-risk DTC in the pediatric population. Patients and Methods: The subjects were 153 patients with DTC ≤ 18 years old, including 58 patients ≤ 15 years old and 136 females, who underwent initial curative surgery in our hospital between 1979 and 2014. Underlying pathology was papillary carcinoma in 130 patients and follicular carcinoma in 23. Risk factors related to disease free survival (DFS) were analyzed and risk stratification was performed. RESULTS: No patient died of the disease and 34 patients (22.2%) developed recurrences. At initial surgery, 30 patients (19.6%) had lymph node metastases diagnosed before initial surgery (cN1) and 9 (5.9%) had gross extrathyroidal extension (ETE). Significant factors related to DFS on multivariate analysis were cN1, ETE, and number of metastatic lymph nodes (NMLNs) ≥ 10, including microscopic MLNs. According to these factors, subjects were divided into 3 categories: low risk (no risk factors, n=89); intermediate risk (1 risk factor, n=37); and high risk (≥ 2 risk factors, n=27). Ten-year DFS rates in the low-, intermediate-, and high-risk groups were 96%, 83%, and 48%, respectively. Only 12% of low-risk patients underwent total thyroidectomy. Since NMLNs become obvious only after surgery, another analysis after excluding “NMLNs” as a factor showed that cN and ETE were significant factors related to poor DFS. According to these 2 factors, risk stratification was attempted in the same manner. Ten-year DFS rates in the low- (no risk factor, n=117), intermediate- (1 risk factor, n=29), and high-risk (2 risk factors, n=7) groups were 92%, 59%, and 43%, respectively. Only 12% of low-risk patients underwent total thyroidectomy. CONCLUSION: For low-risk patients, lobectomy may be sufficient as the initial surgical procedure.

Although advanced thyroid carcinoma patients who cannot be cured by conventional therapy have lacked effective treatment, multitargeted tyrosine kinase inhibitors have recently become available. Phase 3 trials of lenvatinib showed a median time to objective response of 2 (95 % confidence interval (CI) 1.9-3.5) months, demonstrating that shrinks tumors rapidly. The phenomenon of immediate tumor shrink is known as early tumor shrinkage (ETS) which is related to clinical outcome in other malignancies. However, precisely when within 8 weeks lenvatinib starts to affect tumors remains unclear. In tumors near the carotid arteries, trachea, or esophagus, a rapid therapeutic effect can induce fistula formation or arterial bleeding. To prevent such treatment-emergent serious adverse events (SAE), early imaging evaluation seems to be very important. In this study, the point in time when lenvatinib started to shrink tumors was retrospectively investigated. The subjects were 16 patients who started lenvatinib administration between May and August 2015. Tumor size was evaluated by computed tomography (CT) scans frequently within the first 8 weeks according to the Response Evaluation Criteria In Solid Tumors (RECIST) guideline. Initial tumor response was defined as ≥ 10% tumor reduction. Serum thyroglobulin (Tg) level was monitored in 8 differentiated thyroid carcinoma (DTC) without TgAb patients. At the first evaluation, 13 patients (83.3 %) showed tumor reduction and that decreased with time. Thirteen patients (83.3 %) showed >10 % tumor reduction within 8 weeks. In all DTC patients, serum Tg level was markedly decreased. In conclusion, lenvatinib immediately shrinks tumors, the so-called ETS phenomenon. Therefore, careful attention should be paid to fistula formation from the early phase.