Cutoff Age Between Pediatric and Adult Thyroid Differentiated Cancer: Is 18 Years Old Appropriate?

An individualized protein-based prognostic model to stratify pediatric patients with papillary thyroid carcinoma

Pediatric papillary thyroid carcinomas (PPTCs) exhibit high inter-tumor heterogeneity and currently lack widely adopted recurrence risk stratification criteria. Hence, we propose a machine learning-based objective method to individually predict their recurrence risk. We retrospectively collect and evaluate the clinical factors and proteomes of 83 pediatric benign (PB), 85 pediatric malignant (PM) and 66 adult malignant (AM) nodules, and quantify 10,426 proteins by mass spectrometry. We find 243 and 121 significantly dysregulated proteins from PM vs. PB and PM vs. AM, respectively. Function and pathway analyses show the enhanced activation of the inflammatory and immune system in PM patients compared with the others. Nineteen proteins are selected to predict recurrence using a machine learning model with an accuracy of 88.24%. Our study generates a protein-based personalized prognostic prediction model that can stratify PPTC patients into high- or low-recurrence risk groups, providing a reference for clinical decision-making and individualized treatment.

A novel risk stratification model based on tumor size and multifocality to predict recurrence in pediatric PTC: comparison with adult PTC

Background

Pediatric papillary thyroid cancer presents with a more advanced stage of disease than adult PTC; and it is more likely to be aggresive and distant metastases, although the survival rate is high.

Methods

A retrospective observational study was performed in children and adults with PTC. Fisher's exact, chi-square, and rank-sum tests were used to examine the differences. Univariate and multivariate Cox regression analyses were applied to determine the possible risk factors for prognosis. A Kaplan-Meier curve analysis was performed to investigate the relationship between the clinicopathological characteristics and recurrence rate.

Results

The study involved 156 children and 1,244 adults with PTC. Compared to the group without recurrence, proportions of tumors measuring > 1 cm (48.3% vs. 90.9%) and multifocality (30.3% vs. 63.6%) were higher, N1b stage occurred more frequently (33.8% vs. 100%). However, among adult PTC patients, those with recurrence were older (76.1% vs. 59.4%) than those without recurrence. Risk factors for pediatric PTC recurrence included tumor size and multifocality. However, in adult PTC, the risk factor was LLNM. The newly constructed Stratification.N showed better performance, as illustrated by the fact that patients who were classified into Stratification.N 3 showed an obviously poorer prognosis (P=0.01 and P=0.00062), especially in those aged >14 years (P=0.0052).

Conclusion

Compared with adult PTC, pediatric PTC showed unique characteristics in terms of clinical pathology and recurrence. Tumor size and multifocality were strong risk factors for pediatric PTC. Accordingly, the novel proposed risk stratification method could effectively predict the recurrence of pediatric PTC.

Is Multifocality a Predictor of Poor Outcome in Childhood and Adolescent Papillary Thyroid Carcinoma?

CONTEXT

Total thyroidectomy in pediatric papillary thyroid carcinoma (PTC) is recommended in national guidelines because of the high incidence of multifocal disease (MFD).

OBJECTIVE

To determine the incidence of MFD in childhood and adolescent vs adult PTC and whether MFD is a predictor for poorer outcomes in childhood and adolescent PTC.

METHODS

We conducted an institutional review board-approved review of patients with PTC undergoing surgery (1986-2021) at Memorial Sloan Kettering Cancer Center. Clinical and pathological characteristics in patients with unifocal disease (UFD) and MFD were compared using Pearson's χ2 test. Survival outcomes were analyzed using the Kaplan-Meier method and log-rank test. Multivariate analysis assessed the impact of MFD on outcome.

RESULTS

MFD was less common in childhood and adolescent patients with PTC (45%; 127/283) than in adults (54%; 3023/5564; P = .002). Childhood and adolescent patients with UFD and MFD had similar tumor stage and PTC subtype at presentation, with no significant difference in histopathologic features. Median follow-up was 68 months. There was no significant difference in 5-year recurrence-free probability and overall survival was 100% in both groups. There was no significant difference in 5-year contralateral lobe PTC-free probability between patients with UFD and MFD treated with lobectomy. Multivariate analysis showed MFD was not a predictor for recurrence.

CONCLUSION

MFD was less common in childhood and adolescent patients with PTC than adults and was not a predictor of poor outcome on multivariate analysis, with excellent long-term outcomes in all patients with PTC. MFD does not appear to warrant completion thyroidectomy in childhood and adolescent patients selected for lobectomy.

Appropriateness of 14-year cutoff in pediatric differentiated thyroid cancer: Comparison of clinical characteristics and long-term outcomes in 14 years and younger and 15-18 years age groups

BACKGROUND

Pediatric differentiated thyroid cancers (DTCs) differ in pathophysiology, presentation, and clinical outcomes from adult DTCs. However, the cutoff age for defining pediatric DTCs remains debatable, with the American Thyroid Association (ATA) and International Incidence of Childhood Cancer (IICC) report recommending different cutoffs of 18 and 14 years, respectively. In this study, we investigated the appropriateness of 14-year cutoff by comparing the clinical characteristics and long-term outcomes in the 14 years and younger and 15-18 years age groups.

METHODS

Data of DTC patients, aged 18 years and older, from 1981 to 2016, were sequentially extracted and compared between two age groups: ≤14 and 15-18 years.

RESULTS

Total of 176 pediatric DTC patients were included (age group ≤14 years: n = 75; age group 15-18 years: n = 101). None of the baseline clinical characteristics were significantly different between the two age groups. At 2-year follow-up, patients in the age group ≤14 years had significantly higher incomplete response rate compared to those in the age group 15-18 years (69% vs. 42%, respectively, p < .001). However, over a median follow-up of 10.6 years (interquartile range: 7.7-15.5), the 5- and 10-year Disease-free survival (DFS) probabilities were not significantly different (p = .406). On multivariate analysis, incomplete response at 2-year follow-up was the sole independent predictor of poor DFS (hazard ratio: 5.85, 95% confidence interval: 1.69-20.23).

CONCLUSIONS

Subdivision of pediatric DTCs into less than or equal to 14 years and 15-18 years age groups did not have any long-term predictive value. The cutoff of 18 years as recommended by ATA is reasonable and should be uniformly followed to avoid inconsistencies and confusion.

Differentiated Thyroid Cancer in Adolescents: Single Center Experience and Considerations for Surgical Management and Radioiodine Treatment

Objective

Differentiated thyroid cancer (DTC) in adolescents rare but with a favorable outcome, despite higher rates of cervical lymph node and pulmonary metastasis compared to adults. The aim of this study was to critically evaluate treatment of adolescents with DTC at a single center.

Methods

Patients receiving postoperative radioiodine treatment (RAIT) for DTC between 2005 and 2020 at our institution were screened to identify adolescents according to the World Health Organization definition (10-19 years of age). Demographics, clinico-pathological characteristics, treatment and outcome were analyzed.

Results

Among 1,897 DTC patients, 23 (1.3%) were adolescents with a median (range) age of 16 (10-18) years. The female to male ratio was 3.6:1. Sixty percent had classic papillary thyroid cancer, with follicular variant in 40%, which was higher than previously reported (15-25%) for this age group. pT-status was pT1 in 9 (39.2%), pT2 in 8 (34.8%), pT3 in 3 (13%) and pT4 in 3 (13%) patients. In 19 (82.6%) patients, central lymphadenectomy was performed and metastasis was seen in 57%. All patients received RAIT with initial activities of 1.2 (n=1, 4.3%), 2 (n=12, 52.2%) or 3.7 GBq (n=10, 43.5%). Eighteen (78.2%) patients were free of biochemical and radiologic disease at a median follow-up of 60.7 months. Second-line surgery for lymph node relapse was necessary in 3 (13%) cases. There was one disease-associated death.

Conclusion

Despite high rates of metastasis, most patients were cured, and second-line surgery was rarely required. Further prospective studies are needed to determine whether less aggressive surgical management or omitting adjuvant RAIT are feasible in patients with limited stages at diagnosis.

Ultrasound, laboratory and histopathological insights in diagnosing papillary thyroid carcinoma in a paediatric population: a single centre follow-up study between 2000-2022

Background

Papillary thyroid carcinoma (PTC) often coincides with autoimmune thyroiditis (AIT); whether this association is incidental or causal remains debated.

Objective

To evaluate the ultrasonographic, laboratory, and histopathological features of PTC in paediatric patients with and without AIT and its relationship to puberty.

Design

A retrospective cohort study.

Patients and methods

A retrospective analysis of medical records of 90 patients (69; 76.7% females). The mean age at PTC diagnosis was 13.8 years [range 6-18]. All patients were evaluated ultrasonographically before thyroid surgery. Thyroid nodules were categorised using the European Thyroid Imaging Reporting and Data System (EU-TIRADS PL), and cytopathology was assessed using Bethesda criteria. Neck ultrasound results and thyroid and autoimmune status were correlated with histopathological PTC assessment.

Results

The coexistence of PTC and AIT was found in 48.9% (44/90) of patients. The percentage of AIT was increasing with age; AIT was present only in 1/3 of prepubertal, close to 50% in pubertal, and over 60% in adolescent patients. The youngest patients (aged <10 years old) presented more often with goitre and lymphadenopathy and less often with AIT than adolescents (15-18 years of age). There were no differences in TPOAb, TgAb, and TSH levels between the age subgroups. Presurgical TgAb levels were higher than those of TPOAb in the youngest patients. Histopathological analysis revealed that the solid subtype was observed more often in prepubertal children and diffuse sclerosing in children below 14 years of age, whereas the classic subtype dominated in late pubertal. Univariate and multivariate analyses revealed that lymph nodes metastases (LNM) were associated with PTC diameter and fT4 level, whereas extrathyroidal extension with age and angioinvasion with PTC diameter and age. The correlations between age and fibrosis, and the presence of psammoma bodies in malignant tissues were close to significant. We did not observe an association between TSH levels and the presence of autoimmunity and PTC variables.

Conclusions

In paediatric patients the natural course of PTC may be less aggressive in adolescent patients than in younger children (especially < 10 years of age). We suggest that pre-operative evaluation of paediatric patients with thyroid nodules could include apart from assessment of thyroid hormones, evaluation of TPOAb, TgAb, and TRAb together with comprehensive neck ultrasonography.

Thyroid Nodules and Follicular Cell-Derived Thyroid Carcinomas in Children

Although pediatric thyroid tumors have many similarities to those occurring in adults, significant differences are also recognized. For example, although thyroid nodules in children are much less common than in adults, a higher percentage is malignant. Moreover, while pediatric papillary thyroid carcinoma (PTC) is associated with more advanced disease, death due to disease in children and adolescents is very rare, even when distant metastases are present. Some subtypes of thyroid carcinoma, like diffuse sclerosing variant, are especially common in children and adolescents. Moreover, certain histologic findings, such as a tall cell morphology or increased mitotic activity, may not carry the same prognostic significance in children as in adults. Recent studies exploring the molecular underpinnings of pediatric thyroid carcinoma indicate that while driver alterations of thyroid tumorigenesis in children and adults are essentially the same, they occur at very different frequencies, with translocation-associated tumors (most commonly harboring RET and NTRK fusions) comprising a sizable and distinct group of pediatric PTC. DICER1 mutations, an infrequent mutation in adult thyroid tumors, are relatively frequent in pediatric encapsulated follicular-patterned thyroid tumors (with or without invasion or nuclear features of PTC). Additionally, tumor predisposition syndromes (most notably DICER1 syndrome and PTEN hamartoma tumor syndromes such as Cowden syndrome) should be considered in children with thyroid tumors, especially follicular-patterned thyroid tumors and poorly differentiated thyroid carcinoma. This review will explore the current state of knowledge of thyroid nodules and carcinomas in children and adolescents.

Outcomes of the Tall-Cell Variant of Papillary Thyroid Carcinoma in Patients with Different Ages: A 17-Year Mono-Institutional Experience

The tall-cell variant of papillary thyroid carcinoma (TCPTC) is the most common aggressive variant of papillary thyroid carcinoma (PTC) and typically occurs in older patients. In this study, we analyzed retrospectively the largest mono-institutional series of PTCs with tall-cell features (989 patients) over a 17-year period, re-evaluating tumors based on age at presentation and outcomes in different age groups. We divided patients into three age groups following different criteria (the criterion from the American Joint Committee on Cancer Tumor Node Metastasis (AJCC TNM) guidelines, criterion for the statistical division into tertiles and adolescent/post-adolescent criterion) to analyze the clinicopathological characteristics in different age groups, especially in terms of recurrence-free survival (RFS) and distant recurrence-free survival (DRFS). We obtained three main results: 1. the population is distributed among the different age groups, and therefore, this type of cancer is not exclusively found among those of an older age; 2. in the RFS analysis, we can see a higher probability of local recurrence in the younger and older groups and, unexpectedly, a lower probability of local recurrence in the “median age” group; and 3. in the DRFS analysis, we can observe a higher probability of distant recurrence in older patients. From a molecular perspective, no significant differences in the mutational status of BRAF were detected according to different age groups, while mutations in the TERT promoter were exclusively present in older patients of all age groups, highlighting the potential prognostic implications of TERT promoter mutations in PTCs. In conclusion, the results of this series confirm that TC morphology alone in PTCs does not have the same negative prognostic significance in the younger population as in the older population. The reason for these different outcomes remains unclear and needs further studies.

Thyroid Nodules on Ultrasound in Children and Young Adults: Comparison of Diagnostic Performance of Radiologists' Impressions, ACR TI-RADS, and a Deep Learning Algorithm

BACKGROUND. In current clinical practice, thyroid nodules in children are generally evaluated on the basis of radiologists' overall impressions of ultrasound images. OBJECTIVE. The purpose of this article is to compare the diagnostic performance of radiologists' overall impression, the American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS), and a deep learning algorithm in differentiating benign and malignant thyroid nodules on ultrasound in children and young adults. METHODS. This retrospective study included 139 patients (median age 17.5 years; 119 female patients, 20 male patients) evaluated from January 1, 2004, to September 18, 2020, who were 21 years old and younger with a thyroid nodule on ultrasound with definitive pathologic results from fine-needle aspiration and/or surgical excision to serve as the reference standard. A single nodule per patient was selected, and one transverse and one longitudinal image each of the nodules were extracted for further evaluation. Three radiologists independently characterized nodules on the basis of their overall impression (benign vs malignant) and ACR TI-RADS. A previously developed deep learning algorithm determined for each nodule a likelihood of malignancy, which was used to derive a risk level. Sensitivities and specificities for malignancy were calculated. Agreement was assessed using Cohen kappa coefficients. RESULTS. For radiologists' overall impression, sensitivity ranged from 32.1% to 75.0% (mean, 58.3%; 95% CI, 49.2-67.3%), and specificity ranged from 63.8% to 93.9% (mean, 79.9%; 95% CI, 73.8-85.7%). For ACR TI-RADS, sensitivity ranged from 82.1% to 87.5% (mean, 85.1%; 95% CI, 77.3-92.1%), and specificity ranged from 47.0% to 54.2% (mean, 50.6%; 95% CI, 41.4-59.8%). The deep learning algorithm had a sensitivity of 87.5% (95% CI, 78.3-95.5%) and specificity of 36.1% (95% CI, 25.6-46.8%). Interobserver agreement among pairwise combinations of readers, expressed as kappa, for overall impression was 0.227-0.472 and for ACR TI-RADS was 0.597-0.643. CONCLUSION. Both ACR TI-RADS and the deep learning algorithm had higher sensitivity albeit lower specificity compared with overall impressions. The deep learning algorithm had similar sensitivity but lower specificity than ACR TI-RADS. Interobserver agreement was higher for ACR TI-RADS than for overall impressions. CLINICAL IMPACT. ACR TI-RADS and the deep learning algorithm may serve as potential alternative strategies for guiding decisions to perform fine-needle aspiration of thyroid nodules in children.

Radioactive Iodine-Refractory Pulmonary Metastases of Papillary Thyroid Cancer in Children, Adolescents, and Young Adults

CONTEXT

Few studies have explored radioactive iodine-refractory (RAIR) disease in children, adolescents, and young adults with papillary thyroid cancer (CAYA-PTC).

OBJECTIVE

This study systematically investigated the clinicopathologic characteristics and prognosis of CAYA-PTC with RAIR disease.

METHODS

Sixty-five patients with PTC aged ≤20 years were enrolled in this study, and all patients were confirmed to have pulmonary metastases. Clinicopathologic profiles were compared between the radioactive iodine-avid (RAIA) and RAIR groups. Univariate and multivariate regression analyses were performed to identify risk factors for RAIR status and progressive disease (PD). Gene alterations were detected in 17 patients.

RESULTS

Overall, 20 patients were included in the RAIR group, accounting for 30.8% (20/65) of all patients. No significant difference in pathologic characteristics was observed between patients aged <15 years and patients aged 15-20 years, but younger patients were more likely to develop RAIR disease (hazard ratio [HR] 3.500, 95% CI 1.134-10.803, P = .023). RET fusions were the most common genetic alterations in CAYA-PTC, but an association with RAIR disease was not detected (P = .210). RAIR disease (HR 10.008, 95% CI 2.427-41.268, P = .001) was identified as an independent predictor of PD. The Kaplan-Meier curve revealed a lower progression-free survival (PFS) and disease-specific survival (DSS) rate in the RAIR group than in the RAIA group (P < .001 and P = .039). Likewise, RAIR disease was a risk factor for unfavorable PFS in patients aged <15 years (P < .001).

CONCLUSION

RAIR disease occurs in one-third of CAYA-PTC with pulmonary metastases. Younger patients (aged < 15 years) are more susceptible to RAIR status, which leads to unfavorable PFS and DSS.

Cytological evaluation of thyroid nodules in children and young adults: a multi-institutional experience

PURPOSE

The utility of the Bethesda system for reporting thyroid cytopathology is debatable in determining the risk of malignancy in pediatric patients. Moreover, the upper age limit for defining the pediatric group has varied across different studies. The aim of this study is to compare the risk of malignancy (ROM) and risk of neoplasia (RON) across different Bethesda categories between the pediatric, young adult, and adult patients.

METHODS

This is a retrospective multi-institutional study performed in three Indian hospitals. ROM was calculated and compared across Bethesda categories in adult (>18 years) and pediatric age groups (≤18 years), with a subgroup analysis in young adults (19-21 years).

RESULTS

Thyroid nodules from a total of 5958 patients were subjected to fine needle aspiration. Of these 199 were pediatric (3.3%) and follow-up histology was available in 2276. The ROM and RON rates, including overall ROM/RON, were significantly higher in pediatric age group as compared to adults. Overall ROM of suspicious for malignancy and malignant categories was higher in children as compared to adults. The overall surgical resection rates were also higher in pediatric patients (45.2% vs. 35.7%; p < 0.01). The similar trend of increased ROM, RON and resection rates was seen among young adults as compared to adult age group.

CONCLUSION

Thyroid nodules presenting in children are more likely to be malignant than those in adults. Importantly, the young adult group behaved in a similar manner with regard to surgical resection rates, ROM and RON to pediatric.

Fourteen years old as the best age cutoff to differentiate prepubertal from pubertal papillary thyroid carcinoma

BACKGROUND

It is unclear whether differences in clinical presentation and/or prognosis exist between prepubertal papillary thyroid cancer (PTC) and pubertal PTC. At present, there is a lack of definition for the appropriate cutoff age to define prepubertal PTC.

METHODS

This study retrospectively reviewed 227 pediatric PTC patients (aged ≤18 years) who underwent initial surgery from March 2000 to December 2018. The median duration of follow-up was 85 months (range, 8-258).

RESULTS

The age range was basically linearly related to multiple risk factors, such as T3-T4 disease, distant metastasis. Age (p = 0.032) was an independent risk factor for recurrence and persistent disease. Patients aged <14 years had obviously higher rates of extensive disease. The 10-year disease-free survival (DFS) rate of patients aged <14 years was 59.5% and that of patients aged ≥14 years was 82.6% (p = 0.004).

CONCLUSIONS

Fourteen years of age may be an appropriate cutoff to differentiate prepubertal PTC from pubertal PTC.

Molecular Landscape of Pediatric Thyroid Cancer: A Review

Thyroid carcinomas (TC) are rare in the pediatric population; however, they constitute the most common endocrine malignancy. Despite some similarities with adult carcinomas, they have distinct clinical behavior and responses to therapy due to their unique pathology and molecular characteristics. The age cut-off used for defining the pediatric age group has been variable across different studies, and the universally accepted recommendations influence accurate interpretation of the available data. Moreover, factors such as radiation exposure and germline mutations have greater impact in children than in adults. Papillary TC is the most common and the most evaluated pediatric TC. Others, including follicular, poorly differentiated and medullary carcinomas, are rarer and have limited available literature. Most studies are from the West. Asian studies are primarily from Japan, with few from China, India, Saudi Arabia and Republic of Korea. This review provides a comprehensive account of the well-established and novel biomarkers in the field, including point mutations, fusions, miRNA, and thyroid differentiation genes. Familial and syndromic associations are also discussed. Current management guidelines for pediatric patients are largely derived from those for adults. An awareness of the molecular landscape is essential to acknowledge the uniqueness of these tumors and establish specific diagnostic and therapeutic guidelines.

Diagnostic performance of the 2021 Korean thyroid imaging reporting and data system in pediatric thyroid nodules

OBJECTIVES

To evaluate the diagnostic performance of 2021 K-TIRADS biopsy criteria for detecting malignant thyroid nodules in a pediatric population, making comparisons with 2016 K-TIRADS.

METHODS

This retrospective study included pediatric patients with histopathologically confirmed diagnoses. The diagnostic performance of 2021 K-TIRADS was compared with that of 2016 K-TIRADS. Simulation studies were performed by changing biopsy cut-off sizes for K-TIRADS 5 to 1.0 cm (K-TIRADS_5-1.0cm) and 0.5 cm (K-TIRADS_5-0.5cm), and for K-TIRADS 4 to 1.0 cm (K-TIRADS_4-1.0cm) and 1.0-1.5 cm (K-TIRADS_4-1.0~1.5cm). Subgroup analysis was performed in small (< 1.5 cm) and large nodules (≥ 1.5 cm).

RESULTS

Two hundred seventy-seven thyroid nodules (54.9% malignant) from 221 pediatric patients were analyzed. All simulated 2021 K-TIRADS showed higher accuracy than 2016 K-TIRADS. Compared with 2021 K-TIRADS_5-1.0cm, 2021 K-TIRADS_5-0.5cm showed lower specificity (51.6% vs. 47.9%; p = 0.004) but higher sensitivity (77.2% vs. 90.3%; p < 0.001) and accuracy (62.7% vs. 68.9%; p < 0.001). Compared with 2021 K-TIRADS_4-1.0cm, 2021 K-TIRADS_4-1.0~1.5cm showed higher specificity (44.9% vs. 47.9%; p = 0.018) without significant difference in other diagnostic measures. Compared with 2016 K-TIRADS, 2021 K-TIRADS (biopsy cut-offs, 0.5 cm for K-TIRADS 5; 1.0-1.5 cm for K-TIRADS 4) showed higher sensitivity (34.0% vs. 67.3%; p < 0.001) while maintaining specificity (89.4% vs. 88.2%; p = 0.790) in small nodules, and higher specificity (5.9% vs. 25.4%; p < 0.001) while maintaining sensitivity (100% vs. 98.7%; p = 0.132) in large nodules.

CONCLUSIONS

In pediatric patients, 2021 K-TIRADS showed superior diagnostic accuracy to 2016 K-TIRADS, especially with a biopsy cut-off of 0.5 cm for K-TIRADS 5 and 1.0-1.5 cm for K-TIRADS 4.

KEY POINTS

• All simulated 2021 K-TIRADS showed higher accuracy than 2016 K-TIRADS. • 2021 K-TIRADS with cut-off size for K-TIRADS 5 of 0.5 cm showed lower specificity but higher sensitivity and accuracy than that of 1.0 cm. • Compared with 2016 K-TIRADS, 2021 K-TIRADS (biopsy cut-offs, 0.5 cm for K-TIRADS 5; 1.0-1.5 cm for K-TIRADS 4) showed higher sensitivity while maintaining specificity in small nodules, and higher specificity while maintaining sensitivity in large nodules.

Diagnostic Performance of Five Adult-based US Risk Stratification Systems in Pediatric Thyroid Nodules

Background The validation of adult-based US risk stratification systems (RSSs) in the discrimination of malignant thyroid nodules in a pediatric population remains lacking. Purpose To estimate and compare the diagnostic performance of pediatric US RSSs based on five adult-based RSSs in the discrimination of malignant thyroid nodules in a pediatric sample. Materials and methods Pediatric patients (age ≤18 years) with histopathologically confirmed US-detected thyroid nodules at a tertiary referral hospital between January 2000 and April 2020 were analyzed retrospectively. The diagnostic performance of US-based fine-needle aspiration biopsy (FNAB) criteria in thyroid cancer detection was estimated. The following sensitivity analyses were performed: (a) scenario 1: nodules smaller than 1 cm, with the highest category additionally biopsied; (b) scenario 2, application of American College of Radiology Thyroid Imaging Reporting and Data System nodule size cutoffs to other RSSs; (c) scenario 3, scenarios 1 and 2 together. Generalized estimating equations (GEEs) were used for estimation. Results A total of 277 thyroid nodules in 221 pediatric patients (median age, 16 years [interquartile range {IQR}, 13-17]; 172 female; 152 of 277 patients [55%] malignant) were analyzed. The GEE-estimated sensitivity and specificity ranged from 70% to 78% (104 to 119 of 152 patients, based on each reader's interpretation) and from 42% to 78% (49 of 124 patients to 103 of 125 patients). In scenario 1, the missed malignancy rate was reduced from 32%-38% (41 of 134 patients to 34 of 83 patients) to 15%-21% (eight of 59 patients to 28 of 127 patients). In scenario 2, the unnecessary biopsy rate was reduced from 35%-39% (60 of 176 patients to 68 of 175 patients) to 20%-34% (18 of 109 patients to 62 of 179 patients). The highest accuracy was noted in scenario 3 (range, 71%-81%; 199 of 277 patients to 216 of 262 patients). Conclusion The diagnostic performances of the fine-needle aspiration biopsy criteria of five adult-based risk stratification systems were acceptable in the pediatric population and were improved by applying the American College of Radiology Thyroid Imaging Reporting and Data System size cutoff for nodules 1 cm or larger and allowing biopsy of the highest category nodules smaller than 1 cm. © RSNA, 2022 Online supplemental material is available for this article.