Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) in thyroid tumor classification

Prevalence and diagnostic significance of non-invasive follicular thyroid neoplasm with papillary-like nuclear features in Japan-A multi-institutional study

This multi-institutional study investigated non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) frequency and its diagnostic significance in Japan. We reviewed 4008 thyroid nodules resected in six institutions before NIFTP was proposed. Overall, 26 cases diagnosed as non-invasive encapsulated follicular variant of papillary thyroid carcinoma (PTC) and 145 cases of follicular thyroid adenoma (FTA) were included. Of these nodules, 80.8% and 31.0%, respectively, were NIFTPs. In five institutions, NIFTPs were more commonly found in FTA than in PTC nodules. When NIFTP was included with PTC, the overall prevalence was 2.3%, with rates in five institutions below 5.0% (0.8%-4.4%). One NIFTP case with nuclear score 3 revealed nodal metastasis 2.5 years post-resection, and the carcinoma cells were immunohistochemically positive for BRAF. FTAs or NIFTPs with nuclear score 2 did not metastasize. NIFTP was more common among FTA than among PTC nodules, possibly due to underdiagnosis of PTC on nuclear findings. Considering the clinical findings, molecular pathogenesis, and therapeutic strategy in Japan, NIFTP with nuclear score 2 is not different from FTA, and use of this entity terminology is not meaningful. In contrast, NIFTP with nuclear score 3 has potential for metastasis and BRAFV600E mutation. Therefore, in NIFTP cases, nuclear scores 2 and 3 should be separately reported.

The Asian Thyroid Working Group, from 2017 to 2023

The Asian Thyroid Working Group was founded in 2017 at the 12th Asia Oceania Thyroid Association (AOTA) Congress in Busan, Korea. This group activity aims to characterize Asian thyroid nodule practice and establish strict diagnostic criteria for thyroid carcinomas, a reporting system for thyroid fine needle aspiration cytology without the aid of gene panel tests, and new clinical guidelines appropriate to conservative Asian thyroid nodule practice based on scientific evidence obtained from Asian patient cohorts. Asian thyroid nodule practice is usually designed for patient-centered clinical practice, which is based on the Hippocratic Oath, "First do not harm patients," and an oriental filial piety "Do not harm one's own body because it is a precious gift from parents," which is remote from defensive medical practice in the West where physicians, including pathologists, suffer from severe malpractice climate. Furthermore, Asian practice emphasizes the importance of resource management in navigating the overdiagnosis of low-risk thyroid carcinomas. This article summarizes the Asian Thyroid Working Group activities in the past 7 years, from 2017 to 2023, highlighting the diversity of thyroid nodule practice between Asia and the West and the background reasons why Asian clinicians and pathologists modified Western systems significantly.

Clinical Significance of Circulating Tumor Cells (CTCs) and Survivin on Predicting Prognosis in Thyroid Cancer Patients

Background. Clinical significance of circulating tumor cell (CTC) count, mesenchymal CTCs (MCTCs), and survivin in patients with thyroid cancer remains unclear. We evaluated the relationship between the expression of different CTC subtypes or survivin and the prognosis in patients with thyroid cancer. Patients and Methods. This study enrolled 164 patients with thyroid cancer who were diagnosed from January 2013 to September 2020 in our hospital. Among these patients, there were 73 cases with papillary thyroid cancer (PTC), 60 cases with follicular thyroid cancer (FTC), 12 medullary thyroid cancers (MTC), 10 poorly differentiated thyroid cancers (PDTC), 9 anaplastic thyroid cancers, and 10 control patients with nonmalignant thyroid nodules based on their histopathological characteristics. Only 5 milliliters (mL) of peripheral blood from the patients with thyroid cancer and control was used to detect the CTC cell number via CanPatrol capture technique before treatments. We also isolated mononuclear cells (MNC) from the peripheral blood and performed quantity reverse transcriptase polymerase chain reaction (qPCR) for survivin gene expression among these patients. Results. The overall positive rates of CTC at diagnosis were 56.1%. The relapse and metastasis rates in PTC and FTC patients with more than 6 CTCs and positive MCTCs were significantly higher than those in the patients with 6 or less than 6 CTCs and MCTCs. It was also found that these patients with >6 CTCs and MCTCs had shorter progression-free survival (PFS). Additionally, the survivin level of the patients with thyroid cancer was strongly relative to differentiation grades of thyroid cancers. Conclusions. The detection of more than six of total CTCs and positive MCTCs in the patients with differentiated thyroid cancer is an excellent biomarker for predicting the prognosis of patients. Survivin also is a good biomarker for thyroid cancer differentiation.

Have We Got Thy3 Wrong in the UK? A Four-Year Single-Site Analysis of Malignancy Rates in Thy3 Nodules

Introduction

Thyroid nodules routinely undergo ultrasound-guided fine-needle aspiration (FNA), as recommended by the National Institute for Health and Care Excellence (NICE) and the British Thyroid Association (BTA). The cytology results are classified using the “Thy” system from Thy1 to Thy5. Intermediate Thy3 FNA results are challenging, as this suggests malignancy is possible, but the relatively low rates of malignancy can make decision-making difficult. Thy3 is further subdivided into Thy3a and Thy3f.

BTA recommends further ultrasound with or without FNA cytology for Thy3a nodules and hemithyroidectomy for Th3yf nodules based on a published positive predictive value (PPV) for malignancy of 17% for Thy3a and up to 40% for Thy3f results.

We aim to compare the actual malignancy rates of Thy3 nodules in our unit to these figures.

Methods

A retrospective study was performed looking at the histologically confirmed malignancy rates in Thy3a and Thy3f cytology over four years between January 2016 and December 2019.

Results

There were 162 separate Thy3 nodules in 156 patients included in this study, of which 60 were classified as Thy3a and 102 as Thy3f. 10% of patients with Thy3a nodules underwent repeat cytology. The histologically confirmed malignancy rate was 33% in Thy3a and 11% in Thy3f lesions.

Discussion

We found the rates of histologically confirmed malignancy are reversed compared to the published PPVs with a higher rate in Thy3a nodules and a lower rate in Thy3f. This suggests that the surgical decision-making and patient counselling may be based on flawed data in our unit and possibly throughout the UK, making a wider study involving multiple centers desirable.

Solid Thyroid Follicular Nodules With Longitudinal Nuclear Grooves: Clinicopathologic, Immunohistochemical, and Molecular Genetic Study of 18 Cases

CONTEXT.—

Follicular thyroid nodules can be a source of diagnostic difficulties, particularly when they display atypical features commonly associated with malignancy, such as nuclear grooves.

OBJECTIVE.—

To differentiate lesions with atypical features from similar-appearing benign and malignant lesions.

DESIGN.—

Eighteen cases of atypical follicular thyroid nodules characterized by a solid growth pattern and prominent longitudinal nuclear grooves were studied and examined for clinicopathologic characteristics.

RESULTS.—

The lesions occurred in 16 women and 2 men aged 36 to 88 years and measured from 0.2 to 1.5 cm. The tumors were well circumscribed and noninvasive, and histologically characterized by a predominantly solid growth pattern with rare scattered follicles or a combination of solid growth pattern with minor follicular areas. A striking feature seen in all cases was the occurrence of longitudinal nuclear grooves. Immunohistochemical stains showed negativity for cytokeratin 19 (CK19) and HBME-1 in 8 cases; in the other 10, there was focal positivity for HBME-1 in 4 cases and diffuse positivity in 6. All cases were negative for galectin-3 and for CK19, with the exception of 1 case, which was CK19+/HBME-1-. Next-generation sequencing of 16 cases with a 161-gene panel detected 14 single nucleotide variants in 12 cases, predominantly NRAS and HRAS mutations. Clinical follow-up ranging from 18 to 72 months (median, 43.7 months) did not disclose any evidence of recurrence or metastases.

CONCLUSIONS.—

We interpret these lesions as low-grade, indolent follicular proliferations that need to be distinguished from papillary thyroid carcinoma, follicular adenoma, and noninvasive follicular thyroid neoplasms with papillary-like nuclear features.

HBME1 and CK19 expression in non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) vs other follicular patterned thyroid lesions

BACKGROUND

Thyroid neoplasms with follicular architecture can have overlapping morphologic features and pose diagnostic confusion among pathologists. Various immunohistochemical stains have been investigated as potential diagnostic markers for PTC, among which HBME1 and CK19 have gained popularity. Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) poses similar diagnostic challenges with interobserver variability and is often misdiagnosed as adenomatoid nodule or follicular adenoma. This study aims to evaluate expression of HBME1 and CK19 in NIFTPs in comparison to other well-differentiated thyroid neoplasms and benign mimickers.

METHOD

Seventy-three thyroid cases diagnosed over a period of 3 years at Methodist University Hospital, Memphis, TN, USA, were included in this study: 9 NIFTP; 18 papillary thyroid carcinoma (PTC); 11 follicular variant of papillary thyroid carcinoma, invasive (I-FVPTC); 24 follicular adenomas (FA); and 11 multinodular goiters/adenomatoid nodules (MNG). A tissue microarray (TMA) was constructed and HBME1 and CK19 immunohistochemistry was performed.

RESULTS

77.8% of NIFTPs, 88.9% of PTCs, 81.8% of I-FVPTCs, 16.7% of FAs, and 18.2% of MNGs showed HBME-1 expression. 66.7% of NIFTPs, 83.3% of PTCs, 81.8% of I-FVPTCs, 33.3% of FAs, and 45.4% of MNGs expressed CK19. Difference in expression of HBME1 and CK19 was statistically significant for NIFTP vs FA (qualitative; p < 0.05) and NIFTP vs MNG (p < 0.05). No statistically significant difference was found for HBME1 in NIFTP vs PTC (conventional and FVPTC), p ≥ 0.2. Sensitivity of HBME1 and CK19 for NIFTP were 78% and 67%, ~ 88% each for PTC, and 89% and 100% for FVPTC, respectively, while specificity of HBME1 and CK19 for NIFTP were 53% each, ~ 62% each for PTC, and ~55% each for FVPTC.

CONCLUSION

Our study indicated that HBME1 and CK19 are valuable markers in differentiating NIFTPs from morphologic mimics like follicular adenoma and adenomatoid nodules/multinodular goiter. While HBME1 and CK19 are both sensitive in diagnosing lesions with PTC-like nuclear features, CK19 stains a higher number of benign lesions in comparison to HBME1. No increase in sensitivity or specificity in diagnosis of NIFTP, PTC, or FVPTC was noted on combining the two antibodies.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: Epidemiology and Long-Term Outcomes in a Strictly Defined Cohort

Background: A subset of encapsulated/circumscribed follicular variant of papillary thyroid carcinoma (FVPTC) was reclassified as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) in 2016 to reduce overtreatment of a low-risk tumor. Study objectives were to describe the epidemiology and long-term outcomes of NIFTP in a high-volume, urban, tertiary referral center. Methods: Among patients enrolled in the Boston Medical Center (BMC) Thyroid Cancer Registry, 110 cases of FVPTC underwent index thyroid surgery at BMC between 2000 and 2016. Historically, BMC pathologists assess all malignant nodules using sections ≤0.3 cm with evaluation of the entire nodule and capsule. After review of pathology reports to identify potential NIFTPs, slides were rereviewed using criteria established by the NIFTP Working Group in 2016 and 2018. We evaluated interobserver reliability using Cohen's Kappa coefficient. Results: Among 110 FVPTCs, 15 (13%) met NIFTP criteria; 11 women and 4 men, age range 31-64 (mean 47.5) years. Mean tumor diameter was 1.7 cm (compared with 2.2 cm for FVPTC). Among NIFTP cases, there were no lymph node metastases, distant metastases, or tumor recurrences. All NIFTP cases were American Thyroid Association (ATA) low risk compared with only 68% of FVPTC (p = 0.011). Among FVPTCs, 14% had positive lymph nodes at index operation. Four patients (4%) had distant metastases. Mean follow-up time was 46 and 69 months for FVPTC and NIFTP, respectively. Among FVPTCs with an excellent response to therapy (2015 ATA guidelines), there were no recurrences. Just over half (n = 8) of patients with NIFTP received postoperative radioactive iodine (RAI) therapy. Concordance between pathologists was high for ruling out NIFTP (75%), but only 36% for ruling in NIFTP. Overall, for NIFTP designation, Cohen's Kappa was 0.39, which is considered fair. Conclusions: Although this is a relatively small cohort, all NIFTP specimens underwent updated pathology review consistent with current guidelines; mean follow-up was nearly 6 years. NIFTP represents a small fraction of the total papillary neoplasia diagnosed at this tertiary referral center (2.3%). None of the NIFTP cohort experienced an adverse oncologic event, and there were no regional or distant metastases. Over 50% of patients with NIFTP received RAI. Thus, the NIFTP reclassification may substantially reduce the number of patients who require adjuvant therapies, such as completion surgery or RAI.

Updates in the Pathologic Classification of Thyroid Neoplasms: A Review of the World Health Organization Classification

Advances in medical sciences and evidence-based medicine have led to momentous changes in classification and management of thyroid neoplasms. Much progress has been made toward avoiding overdiagnosis and overtreatment of thyroid cancers. The new 2017 World Health Organization (WHO) classification of thyroid neoplasms updated the diagnostic criteria and molecular and genetic characteristics reflecting the biology and behavior of the tumors, and newly introduced the category of borderline malignancy or uncertain malignant potential. Some neoplasms were subclassified, renamed, or redefined as a specific entity. This review introduces changes in the fourth edition WHO classification of thyroid tumors and updates the contemporary diagnosis and classification of thyroid tumors. We also discuss several challenges with the proposal of new diagnostic entities, since they have unique histopathologic and molecular features and clinical relevance.

Risk Stratification of Thyroid Nodules with Bethesda III Category: The Experience of a Territorial Healthcare Hospital

Background The Bethesda System for Reporting Thyroid Cytolopathology (TBSRTC) is the standardized category-based reporting system for thyroid nodule (TN) aspirations; however, atypia of undetermined significance/follicular lesion of undetermined significance (Bethesda category III, AUS/FLUS) is the most controversial category. The aim of this study was to identify the degree of malignancy risk and the related risk factors in the surgical pathology of the Bethesda Category III thyroid nodules.  Methods A total of 4074 patients (15-90 years, 81.5% of females) were subjected to retrospective analysis, and a total of 463 nodules were classified as Bethesda Class III and included in the analysis. Once all the thyroid cytopathological slides and ultrasound (US) reports were reviewed, they were classified according to the Bethesda System for Reporting Thyroid Cytology, the American College of Radiology (ACR) and the Thyroid Imaging Reporting and Data System (TI-RADS). Results Among the 463 Bethesda class III nodules, 167 nodules were surgically excised, showing an overall malignancy of 27.6% (n = 46/167). Patients having thyroid-stimulating hormone (TSH) levels of >4.5 mIU/L (35%), TN <2 cm (34.6%), solid or nearly solid (28.7%), highly hypoechoic (58.3%), longer than wide (50%), lobulated (45.5%), punctate echogenic (48.6%), ACR TI-RAD 5 (55.2%) and falling under the ATA category of high suspicion (50%), displayed a higher risk of malignancy (ROM). The chi-square test revealed a strong association between the echogenicity, echogenic foci, ACR TI-RAD and American Thyroid Association (ATA) category between the malignant and benign nodules. The papillary thyroid carcinoma (PTC) follicular variant (39%) and PTC classical (27%) were identified, in this study population, as the commonest forms of thyroid cancer. Conclusion The nodules with AUS/FLUS cytology malignancy rate are comparable with the earlier estimations of other countries. The ACR TI-RAD displayed more accurate diagnostic performances in predicting malignancy in the Bethesda III nodules. However, to confirm the accuracy of the molecular marker tests in specific cytological scenarios, more extensive studies are required in the future.

Thyroid cytopathology: updates and molecular testing

The utility of fine needle aspiration (FNA) is well described in the context of evaluating thyroid lesions. Among the various international systems of classification of thyroid cytology, the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) has also provided a sound framework to standardize the reporting of FNA cytology results. New molecular evidence and clinical studies demonstrated the need for revision of the nomenclature resulting in introduction of new categories, such as the noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP). Indeterminate thyroid cytology results pose a challenge for further management and the continued development of molecular markers may aid in the management of indeterminate thyroid lesions.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): Update and Diagnostic Considerations-a Review

Advances in our understanding of thyroid lesions, especially those entities with an indolent behavior, has led clinicians to question the most appropriate surgical management of such thyroid nodules. Several studies have shown that the non-invasive encapsulated follicular variant of papillary thyroid carcinomas (NI-EFVPC) exhibits poor histopathologic diagnostic reproducibility and have been over-treated as conventional thyroid cancer. In 2015, an international thyroid working group re-evaluated NI-EFVPC and its diagnostic criteria. The new terminology of "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) was accordingly introduced to replace NI-EFVPC. The literature has emphasized that NIFTPs are biologically similar to follicular adenomas lacking lymph node metastases and/or recurrence. While the definition of NIFTP is based on specific morphological parameters, recent studies have questioned whether the criterion allowing less than 1% of true papillae should be revised to a total absence of papillae. The motivation for this revision is the rare finding, in some studies, of lymph nodes with metastatic NIFTP. This review evaluates the existing published series of NIFTP cases, clinical consequences of NIFTP, and emerging changes in the diagnostic criteria for NIFTP. The introduction of NIFTP has resulted in significant impact on the clinical management of thyroid nodules. Recent revisions in the morphological criteria for NIFTP emphasize the need to adhere to very stringent histomorphologic criteria when making a diagnosis of NIFTP. The adoption of NIFTP terminology instead of NI-EFVPC is associated with conservative lobectomy without radioactive iodine treatment in the majority of cases.

Non-invasive follicular thyroid neoplasm with papillary-like nuclearfeatures (NIFTP): a review and update

BACKGROUND

The nomenclature "Non-invasive Follicular Neoplasm with Papillary-like Nuclear Features (NIFTP)" was introduced in 2016. While NIFTP differs from classic papillary thyroid carcinoma (PTC) in imaging, cytomorphology, histology, molecular profile, treatment, follow up, outcome, and behavior, it largely overlaps with follicular variant of PTC at imaging and cytomorphology. Herein, we review the literature for better understanding NIFTP, and its impact on patient care.

METHODS

The English literature was thoroughly evaluated with the key word of "Noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP)".

OBSERVATIONS

NIFTP presents as a thyroid nodule. On imaging, it is a round-to-oval, well circumscribed mass with solid internal content. Aspirated material shows a microfollicular pattern with focal nuclear features of PTC mostly reported in categories 3-5 of the Bethesda System for Reporting Thyroid Cytology (TBRSTC). NIFTP has decreased risk of malignancy in TBRSTC categories 3-6. Histologic examination of NIFTP reveals an encapsulated neoplasm with follicular pattern and nuclear features of PTC with no capsular or vascular invasion. No papillary structure, atypia, or mitosis is present. In contrast to PTC, only 4% of NIFTP cases harbor a BRAF mutation. Because NIFTP carries an excellent prognosis and indolent behavior, the tumor behavior was changed from malignant to a neoplasm with tumor with extremely indolent behavior. The recommended treatment is lobectomy with no further ablation therapy. Until better understanding of NIFTP, patient's follow up should be occasionally performed by neck ultrasonography and serum thyroglobulin measurement.

CONCLUSION

NIFTP carries an excellent prognosis. It is critical for both clinicians and patients to be aware of extremely indolent behavior of NIFTP in order to prevent unnecessary, aggressive treatment.

New and Emerging Biomarkers in Endocrine Pathology

Significant advances in genomics and molecular genetics in recent years have reshaped the practice of endocrine pathology. Pan-genomic studies, including the pioneering ones on papillary thyroid carcinoma, phaeochromocytoma/paraganglioma, and adrenal cortical carcinoma from the Cancer Genome Atlas (TCGA) project, provided a comprehensive integrated genomic analysis of endocrine tumors into distinct molecularly defined subtypes. Better understanding of the molecular landscape and more accurate definition of biological behavior has been accordingly achieved. Nevertheless, how any of these advances are translated into routine practice still remains a challenge in the era of precision medicine. The challenge for modern pathology is to keep up the pace with scientific discoveries by integrating novel concepts in tumor classification, molecular genetics, prognostication, and theranostics. As an example, pathology plays a role in the identification of hereditary disease, while it offers the tools for complementing molecular genetics, for example, validation of variants of unknown significance deriving from targeted sequencing or whole exome/genome sequencing approach. Immunohistochemistry has arisen as a cost-effective strategy in the evaluation either of somatic mutations in tumors and/or germline mutations in patients with familial cancer syndromes. Herein, a comprehensive review focusing on novel and emerging biomarkers is presented in order pathologists and other endocrine-related specialists to remain updated and become aware of potential pitfalls and limitations in the field of endocrine pathology.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP): a review for clinicians

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is an encapsulated or clearly delimited, noninvasive neoplasm with a follicular growth pattern and nuclear features of papillary thyroid carcinoma (PTC). It is considered a 'pre-malignant' lesion of the RAS-like group. Ultrasonography (US), cytology and molecular tests are useful to suspect thyroid nodules that correspond to NIFTP but there is wide overlap of the results with the encapsulated follicular variant of PTC (E-FVPTC). In these nodules that possibly or likely correspond to NIFTP, if surgery is indicated, lobectomy is favored over total thyroidectomy. The diagnosis of NIFTP is made after complete resection of the lesion by observing well-defined criteria. In the case of patients who received the diagnosis of FVPTC and whose pathology report does not show findings of malignancy (lymph node metastasis, extrathyroidal invasion, vascular/capsular invasion), if the tumor was encapsulated or well delimited, the slides can be revised by an experienced pathologist to determine whether the diagnostic criteria of NIFTP are met, but special attention must be paid to the adequate representativeness of the capsule and tumor. Since NIFTP is not 'malignant', tumor staging is not necessary and patients are not submitted to thyroid cancer protocols or guidelines. We believe that patients with NIFTP without associated malignancy and without nodules detected by US of the remnant lobe (if submitted to lobectomy) can be managed like those with follicular adenoma.

Does Noninvasive Follicular Thyroid Neoplasm With Papillary-Like Nuclear Features (NIFTP) Have a Unique Molecular Profile?

OBJECTIVES

Recognizing preoperative characteristics of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is important for clinical management. Therefore, we assessed presurgical NIFTP molecular profiles using fine-needle aspiration (FNA) material.

METHODS

Presurgical FNA reports of 39 surgically confirmed NIFTP cases from January 2013 through May 2017 were assessed for Afirma and ThyroSeq results.

RESULTS

Twenty-one of 39 NIFTP nodules were preoperatively tested with Afirma with two benign and 19 suspicious results. Twenty-seven of 39 nodules were tested with ThyroSeq (nine of 39 had both Afirma and Thyroseq): 18 (67%) had RAS mutations (13 NRAS, four HRAS, one KRAS), and three of 18 had multiple alterations (NRAS + TP53, n = 1; NRAS + PTEN, n = 2). BRAF T599_R603 + EIF1AX mutation (n = 1), PTEN mutation (n = 1), MET overexpression (n = 1), PAX8/PPARG fusion (n = 3), and THADA/IGF2BP3 fusion (n = 3) comprised the remainder.

CONCLUSIONS

NIFTP cases most commonly displayed suspicious Afirma results and RAS mutations on ThyroSeq, lacking aggressive/BRAF-V600E-like mutations. While NIFTP remains a surgical entity, the lack of aggressive/BRAF-V600E-like mutations can aid in determining the extent of surgery.

Histopathological Diagnostic Criteria for Non-invasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features Highlighted by Six Illustrative Cases

Introduction. The encapsulated, non-invasive subtype of follicular variant of papillary thyroid carcinoma (FVPTC) represents approximately 10% to 20% of all thyroid cancers. Many studies over the past decade have shown that these tumors carry an indolent clinical course, with no recurrence, even in patients treated by lobectomy. Their reclassification as neoplasms with “very low malignant potential” has recently been suggested by an international group of experts and a new terminology was proposed: “non-invasive follicular thyroid neoplasm with papillary-like nuclear features” (NIFTP). However, a diagnosis of NIFTP is still challenging for many pathologists in daily practice. Presentation of case series. By presenting six illustrative cases of NIFTP, this article aims to highlight the diagnostic criteria and the burden difficulties when dealing with NIFTP cases. Characteristic histological features, inclusion and exclusion criteria for NIFTP, as well as sampling guidelines and differential diagnosis challenges are all discussed. Conclusions. The diagnosis of NIFTP is not straightforward and requires meeting strict inclusion and exclusion criteria. Total sampling of the tumor capsule in these cases is mandatory in order to exclude invasion (capsular and/or vascular). A diagnosis of NIFTP promotes a less-aggressive patient management that is, no need for completion thyroidectomy or radioactive iodine therapy.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features: An interobserver study of key cytomorphological features from a large academic medical centre

OBJECTIVE

Because of the indolent nature of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and potential requisite for a more conservative treatment, it is crucial to identify features of this entity preoperatively. Our group recently published findings that there are several cytomorphological features that may be used as clues to distinguish NIFTP, papillary thyroid carcinoma (PTC) and follicular adenoma (FA) on fine needle aspiration. Therefore, we aimed to determine the interobserver reproducibility of these findings.

METHODS

Presurgical fine-needle aspiration slides from NIFTP (n = 30), classic PTC (n = 30) and FA (n = 30) collected from 1/2013-8/2016 were reviewed by seven cytopathologists blindly. Presence of selected cytomorphological features was recorded and compared to determine percent agreement and inter-rater reliability among study cytopathologists using Gwet's AC1 statistics.

RESULTS

For all the cytomorphological features, the overall percent agreement amongst the pathologists ranged between 65.1% and 86.8% (Gwet's AC1 0.30-0.80). There was substantial or almost perfect agreement (Gwet's AC1 > 0.60) in seven cytomorphological features in the classic PTC group, in six features in the NIFTP group and in five features in the FA group. There were no features with poor agreement (Gwet's AC1 < 0.0).

CONCLUSIONS

The current study supports the reproducibility of our previous findings. The high level of agreement amongst pathologists for these groups, and particularly the NIFTP group, supports the notion that when viewed in combination as a cytological profile, these cytomorphological features may assist the cytopathologist in raising the possibility of NIFTP preoperatively. This can potentially aid clinicians in deciding whether more conservative treatment may be appropriate.