Update on follicular variant of papillary thyroid carcinoma with an emphasis on new terminology: noninvasive follicular thyroid neoplasm with papillary-like nuclear features

Papillae, psammoma bodies, and/or many nuclear pseudoinclusions are helpful criteria but should not be required for a definitive cytologic diagnosis of papillary thyroid carcinoma: An institutional experience of 207 cases with surgical follow up

BACKGROUND

Noninvasive follicular thyroid neoplasm with papillary-like features (NIFTP) was introduced in 2016 replacing noninvasive follicular variant of papillary thyroid carcinoma, with recommendations to label them "noncancer." To avoid reducing risk of malignancy (ROM) and overdiagnosing NIFTP as malignant, some authors required restricted cytologic criteria (RC) for a definitive diagnosis of papillary thyroid carcinoma (PTC), including papillae, psammoma bodies. or ≥3 nuclear pseudoinclusions. Since then, NIFTP criteria have been revised, biologic behavior better understood, and incidence reported to be much lower than initially anticipated. This study examines the impact of RC on PTC cytologic diagnoses, ROM, and detection of clinically significant carcinomas (CSC).

MATERIALS AND METHODS

A total of 207 thyroid FNAs originally diagnosed as PTC and suspicious for PTC (SPTC) with surgical follow-up were evaluated. RC were retrospectively applied to cases as a requirement for diagnosing PTC, and cases that did not meet RC were reclassified as SPTC. ROMs and diagnostic accuracies of pre- and post-RC diagnoses were correlated with followup CSC.

RESULTS

RC were met in 118/142 (83%) and 20/65 (31%) of cases originally diagnosed as PTC and SPTC, respectively. Post-RC, 29% (19/65) of CSC originally diagnosed as SPTC were upgraded to PTC, and 17% (24/142) of CSC originally diagnosed as PTC were downgraded to SPTC. No NIFTPs were diagnosed as malignant.

CONCLUSIONS

RC should not be required for a definitive diagnosis of PTC when other nuclear features of PTC are diffuse and overt. Applying RC, however, helps the pathologist arrive at a more definitive diagnosis of PTC in suspicious cases.

WHO 2022 updates on follicular cell and c-cell derived thyroid neoplasm

The latest edition of the WHO Classification of thyroid tumors was released in 2022 and incorporates novel concepts vital to patient management. Thyroid follicular nodular disease is a term used to collectively represent a wide variety of benign and non-neoplastic lesions, including both clonal and non-clonal proliferations that manifest clinically as multinodular goiter. Thyroid neoplasms develop from follicular cells and can be either benign, low-risk, or malignant. To avoid classifying all lesions under 1 cm in diameter as low-risk illnesses, the new classification method highlights the need for subtyping papillary thyroid cancer based on histomorphologic indicators rather than tumor size. Formerly known as the cribriform-morular variety of papillary thyroid carcinoma, this tumor is now more commonly referred to by its more accurate name, cribriform-morular thyroid carcinoma. Its histogenesis is unknown. Similar to the traditional definition of 'poorly differentiated thyroid carcinoma' according to the Turin criteria, the newly defined 'differentiated high-grade thyroid carcinoma' encompasses papillary thyroid cancer, follicular thyroid carcinomas, and oncocytic carcinomas with high-grade characteristics linked to worse prognosis. The squamous cell subtype of anaplastic thyroid cancer has also recently been characterized as a distinct morphologic pattern. In this article, we will discuss the latest revision to the World Health Organization's classification system for thyroid cancer.

Cancer-associated fibroblasts (CAFs) in thyroid papillary carcinoma: molecular networks and interactions

In 1989, Stephen Paget proposed the 'seed and soil' theory of cancer metastasis. This theory has led to previous researchers focusing on the role of a tumour as a cancer seed and antiangiogenesis agents as cancer soil fumigant; for the latter to be effective, it is important for them to be able to distinguish cancer cells from stromal cells. However, antiangiogenesis agents have not produced dramatic survival benefits in vivo. This may be related to their inability to destroy the supporting stroma that promote cancer cell growth. Therefore, in order to effectively arrest cancer cell growth for therapeutic purposes, a paradigm shift is required in our fundamental approach to decipher the molecular events and networks in the stromal environment that cancer cells can thrive and proliferate. The pathogenesis of cancer is a multidimensional process of pathological molecular and cellular pathways, influencing different stromal properties and achieving a mutually negotiated crosstalk between cancer cells and stromal cells. This review summarises the clinical presentation of current knowledge of classical papillary thyroid carcinoma (PTC), emerging molecular diagnostics and future directions of classical PTC research.

Clinical and Molecular Characteristics May Alter Treatment Strategies of Thyroid Malignancies in DICER1 Syndrome

CONTEXT

DICER1 syndrome is a rare autosomal-dominantly inherited disorder that predisposes to a variety of cancerous and noncancerous tumors of mostly pediatric and adolescent onset, including differentiated thyroid carcinoma (DTC). DTC has been hypothesized to arise secondarily to the increased prevalence of thyroid hyperplastic nodules in syndromic patients.

OBJECTIVE

To determine somatic alterations in DICER1-associated DTC and to study patient outcomes.

DESIGN

Retrospective series.

SETTING

Tertiary referral centers.

PATIENTS

Ten patients with germline pathogenic DICER1 variants and early-onset DTC.

METHODS

Somatic DICER1 mutation analysis, extensive somatic DNA variant and gene fusion analyses were performed on all tumors.

RESULTS

Median age at DTC diagnosis was 13.5 years and there was no recurrent or metastatic disease (median follow-up, 8 years). All thyroid specimens showed diffuse nodular hyperplasia with at least one focus suspicious of DTC but without infiltrative growth, extrathyroidal extension, vascular invasion, or lymph node metastasis. Most of the individual nodules (benign and malignant) sampled from the 10 tumors harbored distinct DICER1 RNase IIIb hotspot mutations, indicating a polyclonal composition of each tumor. Furthermore, nine of 10 DICER1-related DTCs lacked well-known oncogenic driver DNA variants and gene rearrangements.

CONCLUSION

On the basis of our clinical, histological, and molecular data, we consider that most DICER1-related DTCs form a low-risk subgroup. These tumors may arise within one of multiple benign monoclonal nodules; thus, hemi-thyroidectomy or, more likely, total thyroidectomy may often be required. However, radioiodine treatment may be unnecessary given the patients' ages and the tumors' low propensity for metastases.

Encapsulated Follicular Variant of Papillary Thyroid Carcinoma Arising in a Follicular Adenoma: a Diagnostic Dilemma

Papillary thyroid carcinoma (PTC) arising within follicular adenoma is a rare histological subset of papillary carcinoma. A 24-year-old female (euthyroid and asymptomatic) presented with a solitary mass in the right lobe of thyroid for 2 years. Fine-needle aspiration cytology (FNAC) suggested features of hyperplasia of thyroid. Hemithyroidectomy was performed. Histopathological examination revealed two distinct areas and was reported as encapsulated variant of papillary carcinoma along with follicular adenoma. Papillary carcinoma was confirmed by positive immunohistochemistry for HBME-1. CT head and neck region ruled out metastasis and the patient was kept on follow-up. There have been reports of medullary and papillary carcinomas occurring together; however, there is a paucity of literature on co-existing follicular neoplasm and papillary carcinoma. We hereby report a rare case of follicular variant of papillary carcinoma arising within follicular adenoma of the thyroid.

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

BACKGROUND

Noninvasive encapsulated follicular variant of papillary thyroid carcinoma (noniEFVPTC) has low risk of adverse outcome in adults, warranting reclassification as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). In children, thyroid nodules have higher risk of malignancy and it is unknown if encapsulated FVPTC (EFVPTC) and infiltrative FVPTC (IFVPTC) tumors have different behavior. We analyzed the clinicopathologic features of follicular variant of papillary thyroid carcinoma (FVPTC) subtypes in our pediatric population to determine if noniEFVPTC has an indolent course as reported in adults.

PROCEDURE

We retrospectively studied all patients diagnosed with FVPTC at our institution. The clinicopathologic characteristics of the histologic subtypes were compared.

RESULTS

Eighteen patients were identified, all treated with total thyroidectomy. No significant differences in age, sex, tumor size, focality, or prior malignancy were detected between subtypes. Extrathyroidal extension had significantly higher incidence in IFVPTC (5/8) compared with EFVPTC (1/10, P = 0.03), translating in significantly more T3 tumors within IFVPTC subtype (5/8), whereas most EFVPTC cases had T1 staging (6/10, T1 vs. T3, P = 0.05). EFVPTC had significantly lower rate of lymph node involvement (N1 in 2/8) compared with IFVPTC (N1 in 8/8, P = 0.003). Only one patient diagnosed with IFVPTC developed extranodal recurrence. When noniEFVPTC and iEFVPTC were separately compared, the noninvasive form showed no propensity for invasive growth (T3 staging: 0/4 vs. 2/6), lymph node metastasis (N1: 0/3 vs. 2/5) or extranodal recurrence.

CONCLUSION

In children, noniEFVPTC/NIFTP has indolent behavior, warranting consideration of less aggressive management, similar to adults.

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP): impact on the reclassification of thyroid nodules

The 2017 edition of the WHO book on Classification of Tumours of Endocrine Organs includes a new section entitled 'Other encapsulated follicular-patterned thyroid tumours', in which the newly created NIFTP (non-invasive follicular thyroid neoplasm with papillary-like nuclear features) is identified and described in detail. Despite deleting the word 'carcinoma' from its name, NIFTP is not a benign tumor either and is best regarded as a neoplasm with 'very low malignant potential'. The main goal of the introduction of NIFTP category is to prevent overdiagnosis and overtreatment. Sampling constraints, especially when dealing with heterogeneous and/or large nodules, and difficulties in the invasiveness evaluation, are the major weaknesses of the histological characterization of NIFTP. At the cytological level, NIFTP can be separated from classic papillary carcinoma (cPTC) but not from encapsulated, invasive follicular variant PTC. The impact of NIFTP individualization for cytopathology is the drop of rates of malignancy for each Bethesda category in general and for indeterminate categories in particular. The biggest impact will be seen in institutions with a high frequency of FVPTC. The introduction of NIFTP has changed the utility of predictive values of molecular tests because RAS mutations and PAX8-PPARg rearrangements are frequently detected in NIFTP. This turns less promising the application of mutation detection panels as indicators of malignancy and will probably contribute to switch to a rule-out approach of molecular testing. Selection for surgery will go on being determined by a combined detection of clinical, cytological and ultrasound suspicious features.

Fine-needle aspirates of thyroid microcarcinoma

INTRODUCTION

Widespread use of ultrasound allows for detection of smaller thyroid nodules and preoperative evaluation with fine-needle aspiration (FNA). Both incidental and non-incidental microcarcinoma can be found, leading to uncertainty with clinical management.

MATERIALS AND METHODS

A retrospective analysis of thyroid FNAs performed at our institution was conducted for the 5-year period from 2010 to 2014. Aspirates were categorized using the Bethesda System for Reporting Thyroid Cytopathology. Cytologic diagnoses were then correlated with final histopathology. Among samples with malignancy on surgical resection, nodules were stratified by size.

RESULTS

A total of 2531 thyroid FNAs were identified; 587 samples had histologic correlation, and 259 malignancies were reported. They were separated into nodules >1 cm (n = 144, 56%) and ≤1 cm (n = 115, 44%). Microcarcinoma was further subdivided into incidental (size ≤0.5 cm, n = 55, 48%) and non-incidental (size >0.5 cm and ≤1 cm, n = 60, 52%). The preoperative cytologic diagnoses for incidental microcarcinoma were: benign (B, n = 11, 20%), follicular lesion of undetermined significance (FLUS, n = 15, 27%), follicular neoplasm (FN, n = 11, 20%), suspicious for malignancy (SM, n = 7, 13%), malignant (M, n = 8, 15%), and nondiagnostic (ND, n = 3, 5%). The FNA categories for non-incidental microcarcinoma were: B (n = 13, 22%), FLUS (n = 3, 5%), FN (n = 3, 5%), SM (n = 10, 17%), M (n = 29, 48%), and ND (n = 2, 3%).

CONCLUSIONS

Incidental microcarcinoma is not an uncommon entity, making up 21% (55 of 259) of malignant nodules on thyroidectomy. Indeterminate diagnoses (FLUS + FN + SM) accounted for the majority (60%) of preoperative FNAs for incidental microcarcinoma, compared with 27% for those of non-incidental microcarcinoma (P < 0.05, χ² test).

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: An Evidence-Based Nomenclature Change

A consensus panel recently used clinical evidence and pathologic parameters to rename noninvasive encapsulated follicular variant of papillary thyroid carcinoma to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) to better reflect the indolent course of this tumor. NIFTP has stringent histopathologic diagnostic criteria established by the panel, including papillary-like nuclear features, and submission of the entire tumor capsule to exclude invasion. From a molecular standpoint, NIFTP is often characterized by RAS-type mutations, similar to other follicular-patterned lesions. While there has been prior evidence in the literature for the low malignant potential of these tumors, projects moving forward will help to independently reinforce the reliability of these criteria and nomenclature. With planned inclusion of NIFTP into the latest World Health Organization endocrine tumor classification scheme, this nomenclature shift provides a model for pathology efforts to refine diagnostic classifications to better guide treatment. In this review we discuss this nomenclature change and review the current literature.

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is a new term replacing what was previously known as non-invasive encapsulated follicular variant of papillary thyroid carcinoma (FVPTC). These tumors show benign/indolent clinical behavior when compared with invasive FVPTC, which led to their reclassification as a "non-malignant" neoplasm. NIFTP shares essentially similar cytomorphologic features as FVPTC, and can only be definitively diagnosed on surgical excision specimens. This article provides an update on morphologic characteristics of NIFTP, along with pertinent molecular studies and management algorithms.