Noninvasive encapsulated follicular variant of papillary thyroid carcinoma: Should it also be reclassified in children?

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.

Non-invasive follicular thyroid neoplasm with papillary-like nuclear feature: clinical, pathological, and molecular update 5 years after the nomenclature revision

The term non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was proposed in 2016 and incorporated as a new entity in the World Health Organization (WHO) classification of tumours of endocrine organs in 2017. Since then, there has been debate regarding the histological criteria for the diagnosis, the need for molecular studies or the risk of lymph node metastasis or recurrence associated with this entity. Over the years, the concept of NIFTP evolved, now including both small (<1 cm) and large (>4 cm) tumours and oncocytic lesions. On the other hand, recent data on NIFTP in the setting of thyroid follicular nodular disease or frequent coexistence of malignant tumours raised concerns regarding the follow-up of these patients. Today, both pathologists and clinicians still face several challenges in the diagnosis, treatment, and follow-up of patients with NIFTP.

Selected Topics in the Pathology of the Thyroid and Parathyroid Glands in Children and Adolescents

The goals of this chapter in keeping with the overall general themes of this special edition will be (1) to highlight aspects of development of the thyroid and parathyroid glands with particular focus on the role and contribution of the neural crest (or not) and how this may impact on the pathology that is seen, (2) to emphasize those lesions particularly more commonly arising in the pediatric population that actually generate specimens that the surgical pathologist would encounter, and (3) highlight more in depth specific lesions associated with heritable syndromes or specific gene mutations since the heritable syndromes tends to manifest in the pediatric age group. In this light, the other interesting areas of pediatric thyroid disease including medical thyroid diseases, congenital hypothyroidism, anatomic variants and aberrations of development that lead to structural anomalies will not be emphasized here.

Case Report: Multifocal non-invasive follicular thyroid neoplasm with papillary-like nuclear features presenting in a female child

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was introduced as a separate entity by the World Health Organization in 2017 with strict inclusion and exclusion criteria.  Most NIFTP cases have been reported in adults and few cases have been diagnosed in children. Here, we present a classic case of NIFTP affecting a 10-year old female child. We also review previous reports of NIFTP in children regarding size, focality, nodal metastasis, recurrence, type of operation and follow-up data. The present report adds a new case of NIFTP in the paediatric age group characterized by multifocality, absence of nodal invasion and indolent course until last follow-up, recommending less aggressive management.

Case Report: Multifocal non-invasive follicular thyroid neoplasm with papillary-like nuclear features presenting in a female child

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was introduced as a separate entity by the World Health Organization in 2017 with strict inclusion and exclusion criteria.  Most NIFTP cases have been reported in adults and few cases have been diagnosed in children. Here, we present a classic case of NIFTP affecting a 10-year old female child. We also review previous reports of NIFTP in children regarding size, focality, nodal metastasis, recurrence, type of operation and follow-up data. The present report adds a new case of NIFTP in the paediatric age group characterized by multifocality, absence of nodal invasion and indolent course until last follow-up, recommending less aggressive management.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): An Update

Based on evidence accumulated over the past three decades showing that noninvasive encapsulated follicular variant of papillary thyroid carcinoma has an indolent clinical behavior and a RAS-like molecular profile similar to follicular adenoma, the Endocrine Pathology Society working group in 2016 proposed to rename this entity as "noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)" in order to eliminate the term "carcinoma" from the diagnosis. It is a major evidence-based attempt initiated by an international group of endocrine pathologists to tackle the epidemic of thyroid cancer overdiagnosis and overtreatment. However, its creation and continuous existence are not without controversies. NIFTP has sparked a wave of follow up studies aiming to decipher the exact nature of this new entity. In this review, we summarize the rationale, diagnostic criteria, controversies and subsequent changes to the NIFTP concept, and their impact on patient care and pathology practice.

Noninvasive Follicular Thyroid Neoplasm With Papillary-Like Nuclear Features in Children: An Institutional Experience and Literature Review

BACKGROUND

Papillary thyroid carcinoma (PTC) in children has a distinctive set of clinicopathologic features and molecular signature compared to their adult counterparts. The recent recommendation to reclassify encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) without invasion as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is based on evidence derived almost exclusively from studies in adults. Clinicopathologic studies restricted to pediatric NIFTP are limited.

METHODS

We retrospectively analyzed all pediatric PTC and NIFTP diagnosed and treated in our institution from 1999 to 2016 (n = 31).

RESULTS

Using recently published consensus diagnostic criteria, we identified 3 NIFTP and 2 infiltrative follicular variants of papillary thyroid carcinoma (FVPTC) among 31 cases. Two of the NIFTP cases were initially diagnosed as EFVPTC. All 3 patients with NIFTP had unifocal tumors of lower American Joint Committee on Cancer (AJCC) classification (T2 or lower) and were free of lymph node or distant metastasis. Total (n = 1) or completion (n = 2) thyroidectomy was performed in all cases, and only 1 NIFTP patient received subsequent radioablative therapy. No residual or recurrent disease has been observed during follow-up (15-138 months) in patients with NIFTP.

CONCLUSIONS

Our experience with NIFTP in children is similar to outcomes reported in adult studies, suggesting that pediatric NIFTP behave indolently as evidenced by the absence of local recurrence in our cohort.

Noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP): a new entity

Since its first official definition in 2016, the new histo-pathological entity of noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP) has attracted much interest among "thyroidologists" worldwide. This is a subset of encapsulated and noninvasive follicular variant papillary thyroid cancer, whose introduction had the intent of de-escalating treatment given its very low malignant potential, approaching to that of follicular adenomas. Many researchers focused on the possibility of preoperatively identifying NIFTP, and investigated their cyto-morphological and molecular characteristics; other ones explored histological and clinical-pathological NIFTP features. Although the majority of published studies confirmed that NIFTP are indolent lesions, some papers did question their low-risk nature. In this brief review, the main aspects of histology, cytology and molecular pathology of NIFTP are discussed based on the current literature.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is rare, benign lesion using modified stringent diagnostic criteria: Reclassification and outcome study

BACKGROUND

Rigid diagnostic criteria for NIFTP have been recently proposed. The frequency of NIFTP using the new criteria is unknown, and whether abortive papillae are associated with BRAF^V600E mutation has not been studied. The aim of this study is to identify NIFTP by a retrospective review of Follicular Variant of Papillary Thyroid Carcinoma (FVPTC), and to study its incidence as well as the association between immunohistochemical BRAF^V600E expression and abortive papillae in NIFTP.

DESIGN

Thyroid tumors diagnosed as FVPTC or NIFTP over a period of 18 years (2000-2017) were identified using the laboratory information system. The final pathology reports were reviewed and potential NIFTP were retrieved. The archived slides for these cases were independently reviewed by 2 pathologists. BRAF^V600E (clone: VE1) immunostain was performed on representative tumor blocks. Clinical information including follow-up data was obtained from the electronic medical records.

RESULTS

Among the 1918 cases with the diagnosis of papillary thyroid carcinoma (PTC), 589 (30.7%) of FVPTC and 136 cases of potential NIFTP were identified. After the review of the archived pathology slides, 29 lesions were morphologically reclassified as NIFTP. Four (13.7%) of these were positive for BRAF^V600E; no association was found between the presence of abortive papillae and BRAF^V600Eexpression (p=0.3). Exclusion of the 4 cases with BRAF^V600Eexpression resulted in 25 lesions of final NIFTP, representing 4.2% of the FVPTC and 1.3% of the PTC. The mean age of the NIFTP patients was 50 years, 87.5% were females. The mean size of the lesions was 1.4 cm (0.1-4.0 cm). Intranuclear pseudoinclusions were not identified, and abortive papillae were identified in 60% of NIFTP. The average follow-up was 70 (28-166) months. There were no adverse events (recurrence or metastasis) in the NIFTP group.

CONCLUSION

When strictly defined, NIFTP comprises 1.3% of cases perviously classified as PTC. In morphological NIFTP, no correlation is found between the presence of abortive papillae and the BRAF^V600E expression. Intranuclear pseudo-inclusions are not observed in NIFTP. Modification of current morphological criteria to include BRAF^V600E immunohistochemistry test may stratify NIFTP with benign outcome.

How Many Papillae in Conventional Papillary Carcinoma? A Clinical Evidence-Based Pathology Study of 235 Unifocal Encapsulated Papillary Thyroid Carcinomas, with Emphasis on the Diagnosis of Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features

Background: The percentage of papillae is a crucial criterion in differentiating noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) from papillary thyroid carcinomas (PTCs) and in subclassifying PTC into classic and follicular variant. Since the description of NIFTP, three studies have shown that the presence of any papillae may be associated with nodal metastasis, which led to modification of the NIFTP criterion from <1% papillae to no true papillae allowed. We aim at providing clinical evidence-based data on the impact that papillary growth has on nodal spread and tumor genotype in tumors previously diagnosed as encapsulated unifocal PTC. Methods: A meticulous histopathologic examination was performed on 235 cases previously diagnosed as unifocal encapsulated PTC (U-EPTC). One hundred of these cases were subjected to BRAF^V600E and NRAS^Q61R immunohistochemistry. Results: In our cohort, 27 patients (12%) had lymph node metastasis (N1) at the time of initial resection. Overall, 89% of the tumors in the N1 group contained ≥50% papillae, compared with 13% in the N0/Nx group. Nodal metastases were only present in tumors with ≥1% papillae. In noninvasive U-EPTC (n = 161), N1 disease was seen only in tumors with ≥10% papillae. A higher percentage of papillae within the tumor also correlated with an increased frequency of BRAF^V600E and decreased rate of NRAS^Q61R. None of the 26 NRAS-positive cases had nodal disease, including the invasive tumors. Among 216 patients with follow-up (median: 5.2 years), 3 patients (1.5%) had distant metastases, all detected at the initial presentation. All three tumors displayed 100% follicular growth, and capsular or vascular invasion. There was no locoregional recurrence in the entire cohort. Conclusion: In U-EPTC, there is a strong correlation between high percentage of papillary growth, presence of nodal metastasis, and BRAF+/RAS- genotype regardless of invasive status. Nodal metastases were not seen in tumors with <1% papillae irrespective of invasive status. These findings indicate that the initial criterion of <1% papillae is still valid for the diagnosis of NIFTP. Reinstituting this criterion will spare a carcinoma diagnosis and unnecessary therapy with its side effects on patients who have negligible clinical risk.

Differences in Thyroid Nodule Cytology and Malignancy Risk Between Children and Adults

Background: The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) is used to interpret fine-needle aspiration (FNA) cytology of thyroid nodules in children and adults. Nodule management is guided by the implied malignancy risk of each cytological category, which has been derived from adult populations. Whether these implied risks are applicable to pediatric thyroid nodules remains uncertain. We compared malignancy rates between pediatric and adult thyroid nodules within each cytological category. Methods: We evaluated consecutive thyroid nodules ≥1 cm that underwent FNA at the Boston Children's Hospital and Brigham and Women's Hospital from 1998 to 2016. All cytology was interpreted by a single cytopathology group according to the BSRTC. Malignancy rates were compared between pediatric (<19 years) and adult (≥19 years) patients. Results: Four hundred thirty pediatric thyroid nodules and 13,415 adult nodules were analyzed. Pediatric nodules were more likely to be malignant than adult nodules (19% vs. 12%, p = 0.0002). Within cytological categories, malignancy rates were higher in pediatric nodules than in adult nodules that were cytologically nondiagnostic (11% vs. 4%, p = 0.03), atypia of undetermined significance (AUS; 44% vs. 22%, p = 0.004), or suspicious for follicular neoplasm (SFN; 71% vs. 28%, p = 0.001). There were no significant differences between children and adults in the types of thyroid cancers diagnosed in these cytological categories. Among cytologically benign nodules, the difference in malignancy rates was statistically significant but clinically minimal (0.7% vs. 1%, p = 0.001). Malignancy rates did not differ between children and adults among nodules with cytology suspicious for papillary carcinoma (73% vs. 68%, p = 0.67) or positive for malignancy (97% vs. 95%, p = 1). Among the subset of nodules that were resected, the malignancy rate was higher in children than in adults only in nodules that were SFN (71% vs. 36%, p = 0.007). Conclusions: Among thyroid nodules that are cytologically AUS, SFN, or nondiagnostic, malignancy rates are higher in children than in adults. These discrepancies likely represent true differences in malignancy risk between pediatric and adult patients, rather than differences in cytological interpretation. Our findings provide pediatric-specific data to inform the optimal management of thyroid nodules in children, which may differ from that of adult nodules with equivalent cytology.