Evaluation of the follicular patterned thyroid lesions based on the WHO 2022 criteria with an emphasis on the grey-zone lesions

Follicular-patterned thyroid nodules (FPTN) are classified byWHO-2022 into benign, borderline and malignant categories. There are however, grey-zone lesions that pose a diagnostic challenge due to ambiguity in defining criteria and inter-observer variability. WHO-2022 has enumerated specific diagnostic criteria for these lesions. Accurate categorization of morphologically similar TNs is vital to reduce overtreatment of indolent lesions. In this study, we have reclassified FPTNs according to WHO-2022 criteria, emphasizing on grey-zone lesions. We studied the utility of immunohistochemistry (IHC)-CD56, HBME-1 and CK19 in distinguishing benign from malignant nodules and BRAFV600E IHC to better distinguish the (widely-invasive) encapsulated follicular variant of papillary thyroid carcinoma (FVPTC) from infiltrative FVPTC. Only those cases with dominant nodule having follicular pattern histology were included and re-evaluated for following histopathological features-focality, encapsulation, circumscription, nuclear PTC features, capsular-invasion, angio-invasion, papillae and necrosis. IHC findings for above-mentioned markers were noted. Seventy-nine cases met the inclusion criteria. Amendment of original diagnosis was done in 19 % cases. BRAFV600E IHC was positive in the two cases of infiltrative FVPTC while it was negative in all nine IE (invasive encapsulated) FVPTCs. Diffuse HBME1 was noted in most malignant nodules (61 %) while CD56 was expressed more often in benign lesions (70 %). CK19 was positive in lesions displaying nuclear PTC features (86 %). Using WHO 2022 criteria, we were able to re-classify follicular thyroid lesions with greater confidence. Appropriate IHC panel in adjunct to histology aids in categorizing challenging cases.

RAS-Mutant Follicular Thyroid Tumors: A Continuous Challenge for Pathologists

The classification of thyroid nodules, particularly those with a follicular growth pattern, has significantly evolved. These tumors, enriched with RAS or RAS-like mutations, remain challenging for pathologists due to variables such as nuclear atypia, invasion, mitotic activity, and tumor necrosis. This review addresses the histological correlates of benign, low-risk, and malignant RAS-mutant thyroid tumors, as well as some difficult-to-classify follicular nodules with worrisome features. One prototypical RAS-mutant nodule is non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). The assessment of nuclear characteristics in encapsulated/well-demarcated non-invasive RAS-mutant follicular-patterned tumors helps distinguish between follicular thyroid adenoma (FTA) and NIFTP. Despite this straightforward concept, questions about the degree of nuclear atypia necessary for the diagnosis of NIFTP are common in clinical practice. The nomenclature of follicular nodules lacking clear invasive features with increased mitotic activity, tumor necrosis, and/or high-risk mutations (e.g., TERT promoter or TP53) remains debated. Invasion, particularly angioinvasion, is the current hallmark of malignancy in RAS-mutant follicular-patterned neoplasms, with follicular thyroid carcinoma (FTC) as the model. Assessing the tumor interface is critical, though full capsule evaluation can be challenging. Multiple levels and NRASQ61R-specific immunohistochemistry can aid in identifying invasion. Controversies around vascular invasion persist, with ancillary stains like CD31, ERG, and CD61 aiding in its evaluation. Moreover, the review highlights that invasive encapsulated follicular variant papillary thyroid carcinoma (IEFVPTC) is closely associated with FTC, suggesting the need for better nomenclature. The concept of "high-grade" differentiated carcinomas, applicable to FTC or IEFVPTC with necrosis and/or high mitotic activity, is also discussed.

THADA-IGF2BP3 gene fusions in thyroid fine needle aspiration is involved in the pathway to "noninvasive follicular thyroid neoplasm with papillary-like nuclear features"

BACKGROUND

The increased usage and adaptation of molecular testing of thyroid fine needle aspirations (FNA) has expanded the variety and number of gene fusions identified. While the identified number of molecular alterations is increasing, the definitive association between preoperative molecular analysis and phenotype has yet to be established. The aim of this study was to examine Thyroid adenoma-associated (THADA)-IGF2BP3 molecular fusions with FNA categorization, surgical pathology diagnosis, and other molecular alterations detected by ThyroSeq Genomic Classifier testing.

METHODS

FNA cytology samples of thyroid nodules from 04/2017 to 01/2023 with the diagnosis of atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS; Bethesda III) or follicular neoplasm suspicious for follicular neoplasm (FN/SFN; Bethesda IV) with associated ThyroSeqV3 testing were reviewed. Parameters including patient demographics, FNA diagnosis, ThyroSeq V3 results, and surgical pathology follow up were examined.

RESULTS

87 out of 249 (35%) FNA specimens of thyroid nodules displayed molecular alterations. 64 cases (74%) had a cytology diagnosis of AUS and 23 (26%) had FN. RAS mutation was observed in 48 cases. On surgical follow-up, 17 (35%) cases showed non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), while 14 (29%) patients had a malignant diagnosis. THADA-IGF2BP3 fusions were seen in 8 cases, all with NIFTP on surgical pathology follow-up (100%).

CONCLUSIONS

Analysis of THADA-IGF2BP3 fusion, in our institutional series, shows close association with NIFTP cases. THADA-IGF2BP3 fusion, which seems to be a favorable prognostic indicator in general, may serve as a molecular marker for non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP).

Seven years of Non-invasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features (NIFTP): Rate of Acceptance and Variation of Diagnostic Approaches Across Different Continents

CONTEXT

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was introduced as a new entity replacing the diagnosis of noninvasive encapsulated follicular variant of papillary thyroid carcinoma (PTC). Significant variability in the incidence of NIFTP diagnosed in different world regions has been reported.

OBJECTIVE

To investigate the rate of adoption of NIFTP, change in practice patterns, and uniformity in applying diagnostic criteria among pathologists practicing in different regions.

METHODS

Two surveys distributed to pathologists of the International Endocrine Pathology Discussion Group with multiple-choice questions on NIFTP adoption into pathology practice and whole slide images of 5 tumors to collect information on nuclear score and diagnosis. Forty-eight endocrine pathologists, including 24 from North America, 8 from Europe, and 16 from Asia/Oceania completed the first survey and 38 the second survey.

RESULTS

A 94% adoption rate of NIFTP by the pathologists was found. Yet, the frequency of rendering NIFTP diagnosis was significantly higher in North America than in other regions (P = .009). While the highest concordance was found in diagnosing lesions with mildly or well-developed PTC-like nuclei, there was significant variability in nuclear scoring and diagnosing NIFTP for tumors with moderate nuclear changes (nuclear score 2) (case 2, P < .05). Pathologists practicing in North America and Europe showed a tendency for lower thresholds for PTC-like nuclei and NIFTP than those practicing in Asia/Oceania.

CONCLUSION

Despite a high adoption rate of NIFTP across geographic regions, NIFTP is diagnosed more often by pathologists in North America. Significant differences remain in diagnosing intermediate PTC-like nuclei and respectively NIFTP, with more conservative nuclear scoring in Asia/Oceania, which may explain the geographic differences in NIFTP incidence.

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

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.

Nodal metastasis in noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

The term noninvasive tumor with a follicular growth pattern and nuclear features of papillary thyroid cancer (NIFTP) is used to describe a tumor currently considered as a pre-malignant lesion for which a conservative therapeutic approach (i.e., lobectomy without radioiodine therapy) is strongly suggested. However, some patients with NIFTP and loco-regional or distant metastases have been already reported. We present an adult male patient with a final histological diagnosis of NIFTP and lymph node metastasis noted at post-therapy whole-body scintigraphy performed some days after radioiodine therapy.

NIFTPs may be reclassified not only from FVPTCs but also from follicular adenomas

Few studies have focused on reclassifying follicular adenomas (FAs) as noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTPs), but none have been conducted in America or Europe. The aims of this study were to analyze the prevalence of NIFTP reclassified from follicular variant of papillary thyroid carcinomas (FVPTCs) and FAs before NIFTP was defined in the literature, the rate of NIFTP among PTC (papillary thyroid carcinomas) established in real time between 2017 and 2022, and demographic, ultrasonographic, and cytologic characteristics of NIFTPs compared with FVPTCs and FAs. This was a retrospective cohort study of tumors diagnosed as PTCs (n = 247) and FAs (n = 144) at a Brazilian hospital. Overall, 13.4% of PTCs and 7% of FAs were reclassified as NIFTPs. The rate of real-time diagnosed NIFTPs among PTC was 12.3%. The median tumor size was larger among NIFTPs (3.0 cm) than FVPTCs (1.1 cm; P < 0.01). A high-risk ultrasonographic pattern was rare in NIFTPs (5.6%). The cytologic classifications differed between FVPTCs and NIFTPs (P < 0.01), and the most frequent category among NIFTPs was 'follicular neoplasm' (52.6%). The category 'suspicious for malignancy' was frequent in FVPTCs and rare (5.3%) in NIFTPs. In conclusion, FVPTCs and FAs may be reclassified as NIFTPs. The prevalence of NIFTPs reclassified from FAs was lower in our cohort than in Asian studies. The rate of NIFTPs reclassified from PTC was similar to that of NIFTPs diagnosed in real time and was aligned with rates reported in studies from America and Europe. Preoperative features could not differentiate NIFTPs from FVPTCs or FAs.

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.

Detailed fine needle aspiration cytopathology findings of noninvasive follicular thyroid neoplasm with papillary-like nuclear features with nuclear grading correlated to that of biopsy and Bethesda category and systematic review

BACKGROUND

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) poses diagnostic challenge in fine needle aspiration cytopathology (FNAC). We aimed first to document our FNAC Bethesda categories (BCs) for all of our NIFTPs and compare our findings with those in the literature with series containing at least 14 cases each.

METHODS

Cases with final histopathological diagnoses of NIFTP and their preoperative FNAC were retrieved from 2006 to 2022 and our cytopathological BCs were documented. Then the slides were re-reviewed in a blinded manner for detailed classification and the results of both the BCs and blinded reclassification were compared with series in the literature for both BCs and detailed cytopathological review of the cases.

RESULTS

Thyroid FNACs of 43 out of 86 patients with final NIFTP diagnoses were obtained. Females composed 72.1% (F/M: 31/12); mean age and mean tumor diameter was 47.6 (19-72 years) and 23.4 mm (7-60 mm), respectively. Totally 81.4% (35/43) were classified in the "indeterminate" diagnostic categories; namely 44.2% (19/43) were reported as atypia of undetermined significance (AUS; BC III), 20.9% (9/43) were follicular neoplasm (FN; BC IV), and 16.3% (7/43) were suspicious for malignancy (SM; BC V). No patient was diagnosed as positive for malignancy (BC VI), preoperatively. Detailed cytomorphologic reevaluation revealed heterogeneous cytopathologic findings and nuclear grade (especially nuclear enlargement, membrane irregularity and elongation) significantly increased with respect to BCs. Systematic review confirmed extremely heterogeneous cytomorphologic nature of NIFTP.

CONCLUSIONS

NIFTPs were categorized most frequently as AUS, followed by FN and SM on FNAC. Our re-review were not able to specify features solely unique to NIFTP alone but may distinguish these cases from classic papillary thyroid carcinoma.

An investigation into noninvasive follicular thyroid neoplasms with papillary-like nuclear features: does the initial proposal on noninvasive follicular thyroid neoplasms with papillary-like nuclear features behavior hold true?

Current management of patients with noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) is lobectomy with close clinical follow-up. Because this entity is still young, we present our 5-year institutional experience with NIFTP since that time. Cases of NIFTP diagnosed from 2017 to 2022 were identified. Data points including patient demographics, radiology, cytologic and pathologic diagnoses, molecular profiles, and clinical follow-up were documented. A literature review of NIFTP case series was performed. A total of 379 cases were included (mean age: 52 years, female:male ratio 3.3:1). Ultrasound findings were available for 260 patients, and 247 underwent fine-needle aspiration (FNA). The FNA diagnoses per the Bethesda System for Reporting Thyroid Cytology were nondiagnostic (n = 2), benign (n = 16), atypia of undetermined significance/follicular lesion of undetermined significance (n = 119), follicular neoplasm/suspicious for follicular neoplasm (n = 68), suspicious for malignancy (n = 31), and malignant (n = 11). Molecular testing was performed in 179 cases. Lobectomy was performed for 183, total thyroidectomy for 192, and nodulectomy for 4 cases. The average size of NIFTP was 2.3 cm, and 232 cases had additional nodules (including benign and malignant neoplasms). Multifocal NIFTP occurred in 32 patients. Lymph nodes were evaluated in 196 cases with metastatic carcinoma in 29 cases (all with concurrent diagnoses of carcinoma). Most patients were alive at follow-up, 100 were lost to follow-up, and three died from other causes. Literature review revealed 2870 NIFTP cases with similar patient demographics and pathologic findings. We confirm that NIFTP is a low-risk neoplasm with indolent clinical behavior, which can be managed conservatively.

The Incidence Trend and Management of Thyroid Cancer-What Has Changed in the Past Years: Own Experience and Literature Review

Because of ambiguous and widely debated observations concerning the incidence, trend, and management of TC, we performed this analysis. We drew attention to some events, such as "cancer screening activity", introduction of noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP) to TC types, possibility of papillary thyroid microcarcinoma (PTMC) active surveillance (AS), occurrence of personalized medicine in TC management, and, finally, COVID-19 pandemic time. Because of the opinion that all changes have been made mostly by PTC, we compared it to the remaining types of TC in terms of incidence, clinical and pathological characteristics, and treatment. We analyzed patients treated in a single surgical center in eastern Europe (Poland). The prevalence of TC significantly increased from 5.15% in 2008 to 13.84% in 2015, and then significantly decreased to 1.33% in 2022 when the COVID-19 pandemic lasted (p < 0.0001). A similar trend was observed for PTC, when the incidence significantly increased to 13.99% in 2015 and then decreased to 1.38% in 2022 (p < 0.0001). At that time, the NIFTP category was introduced, and observation of PTMC began. The prevalence of FTC and MTC also increased until 2015 and then decreased. Significant differences in age, types of surgery, necessity of reoperation, and pTNM between PTCs and other types of TCs were observed. The average age was significantly lower in PTC patients than in patients with the remaining types of TC (p < 0.0001). Four milestones, including NIFTP introduction, the possibility of PTMC AS, personalized cancer medicine, and the COVID-19 pandemic, may have influenced the general statistics of TC.

Identification of NIFTP-Specific mRNA Markers for Reliable Molecular Diagnosis of Thyroid Tumors

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is a low-risk thyroid tumor with a favorable prognosis. Nonetheless, differentiating NIFTP from other thyroid tumors remains challenging, necessitating reliable diagnostic markers. This study is aimed at discovering NIFTP-specific mRNA markers through RNA sequencing analysis of thyroid tumor tissues. We performed mRNA expression profiling for 74 fresh frozen thyroid tissue samples, including NIFTP and benign and malignant follicular-cell-derived tumors. NIFTP/malignant tumors showed 255 downregulated genes and 737 upregulated genes compared to benign tumors. Venn diagram analysis revealed 19 significantly upregulated and 7 downregulated mRNAs in NIFTP. Akaike information criterion analysis allowed us to select OCLN, ZNF423, LYG1, and AQP5 mRNA markers. We subsequently developed a predictive model based on logistic regression analysis using these four mRNAs, which we validated in independent samples (n = 90) using a qRT-PCR assay. This model demonstrated high accuracy in predicting NIFTP in discovery dataset (AUC (area under the receiver operating characteristic) = 0.960) and the validation dataset (AUC = 0.757). Our results suggest that OCLN, ZNF423, LYG1, and AQP5 mRNA markers might serve as reliable molecular markers for identifying NIFTP among other thyroid tumors, ultimately aiding in accurate diagnosis and management of NIFTP patients.

Is it Possible to Diagnose "Non-Invasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features" Preoperatively?

There is no accepted consensus or algorithm for the preoperative diagnosis of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) in patients with thyroid nodules. In this study, we evaluated the importance of preoperative neutrophil-to-lymphocyte ratio and platelet-to-lymphocyte ratio in the differential diagnosis of NIFTP. Pathology preparations of 209 patients with a follicular variant of papillary thyroid carcinoma (FVPTC) diagnosed after thyroid surgery in a tertiary health center between January 2010 and January 2020 were re-evaluated. Patients were divided into NIFTP and encapsulated follicular variant papillary thyroid carcinoma (EFVPTC) to compare. Of the patients, 58 (27.7%) were NIFTP, and 151 (72.3%) were EFVPTC. There was no statistically significant difference in terms of age (p = 0.46), tumor size (p = 0.51), gender (p = 0.48), and surgical technique (p = 0.78) between the groups. The probability of the neutrophil-to-lymphocyte ratio (NLR) > 2 is more common in the EFVPTC group. It was statistically significant that the NIFTP group was 1.96 times more likely to have NLR > 2 (OR: 1.96, 95% CI: 1.06-3.63) (p < 0.05). However, there was no risk difference between the groups in terms of the platelet-to-lymphocyte ratio (PLR) (OR: 0.76, 95% CI: 0.41-1.43) (p > 0.05). The diagnosis of NIFTP should be kept in mind in the evaluation of patients whose thyroid fine-needle aspiration (FNA) biopsy results are in the intermediate group. NIFTP exhibits better prognostic findings than classic thyroid papillary cancer and EFVPTC. Therefore, preoperative diagnosis of NIFTP in line with laboratory, ultrasonography, and FNA findings will save the patient from unnecessary overtreatment.

Preoperative evaluation of thyroid nodules - Diagnosis and management strategies

Thyroid cancer is the most common endocrine malignancy, with increasing incidence over the past few decades. Fine needle aspiration (FNA) biopsy is the gold standard for preoperative diagnosis of thyroid malignancies. Nevertheless, this method renders indeterminate results in up to 30% of the cases. Therefore, these patients are often referred to unnecessary surgery to establish the diagnosis. To improve the accuracy of preoperative diagnosis, several other ways, such as ultrasonography, elastography, immunohistochemical analysis, genetic testing, and core needle biopsy, have been developed and can be used either in association with or as an alternative to FNA. This review aims to evaluate all these diagnostic tools to determine the most appropriate way of managing thyroid nodules and subsequently improve the selection of cases referred to surgery.

A Comprehensive Study on the Diagnosis and Management of Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features

Background: Since the noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTPs) was introduced in 2016, most retrospective studies have included cases diagnosed as encapsulated follicular variant of papillary thyroid carcinoma. We investigate a cohort diagnosed with NIFTP at resection. Methods: Retrospective institutional cohort of NIFTP from 2016 to 2022, including clinical, cytological, and molecular data for 319 cases (6.6% of thyroid surgeries, 183 cases as NIFTP-only). Results: The patient cohort had unifocal or multifocal thyroid nodules. Female:male ratio was 2.7:1, mean age was 52 years and median NIFTP size was 2.1 cm. NIFTP was associated with multiple nodules in 23% patients (n = 73) and 12% of NIFTP were multifocal (n = 39). Fine needle aspiration (FNA) of NIFTP (n = 255) were designated as nondiagnostic = 5%, benign = 13%, atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) = 49%, follicular neoplasm/suspicious for follicular neoplasm (FN/SFN) = 17%, suspicious for malignancy = 12%, or malignant = 4%. Molecular alterations were identified in 93% (n = 114), RAS or RAS-like. Thyroid Imaging Reporting and Data System (TI-RADS) score 4 was recorded in 50% of NIFTP, followed by scores 3 and 5 (26% and 20%, respectively). We also investigated the factors associated with extent of surgery. In our NIFTP-only group (n = 183), 66% were identified after hemithyroidectomy (HT) and 34% after total thyroidectomy (TT). On univariate analysis, TT patients demonstrated higher Bethesda category by FNA, more often had aberrant preoperative thyroid function, and/or underwent an FNA of additional nodule(s). With multivariable regression, Bethesda V NIFTP, in the presence of other nodules being evaluated by FNA and aberrant preoperative thyroid function, independently predicts TT. Bethesda II NIFTP correlated significantly with HT. Fifty-two patients (28%) with NIFTP-only had at least one postoperative surveillance ultrasound. In the NIFTP-only cohort, no HT patients had completion thyroidectomy or received postoperative radioactive iodine. No recurrence or metastases were recorded with median follow-up of 35 months (6-76 months; n = 120). Conclusions: Given this large cohort of NIFTP, including a large subset of isolated NIFTP-only, some with >6 years of follow-up and no tumor recurrences, consensus practical guidelines are needed for adequate postoperative management. Given the American Thyroid Association (ATA) provides guidelines for management of low-risk malignancies, guidance regarding that for borderline/biologically uncertain tumors, including NIFTP, is a reasonable next step.

Challenges in Encapsulated Follicular-Patterned Tumors: How Much Is Enough? Evaluation of Nuclear Atypia, Architecture, and Invasion

Thyroid pathology is notoriously fraught with high interobserver variability, and follicular-patterned tumors are among some of the most challenging to assess accurately and reproducibly. Given that encapsulated or well-circumscribed follicular-patterned tumors often have similar molecular profiles, that is, frequent RAS or RAS-like alterations, the diagnosis usually relies on histopathologic examination alone. Unfortunately, many of the features that are used for diagnosis and prognosis of these tumors have long been controversial and frequently debated topics, both due to their subjectivity and their evolving (or not yet resolved) definitions. In more recent years, the introduction of noninvasive follicular thyroid neoplasm with papillary-like nuclear features has added further complexity to this discussion. In particular, the criteria and significance of nuclear features of papillary thyroid carcinoma, architectural patterns, and invasive growth still pose significant diagnostic challenges and confusion. This review explores some of the challenges in evaluating encapsulated follicular-patterned tumors, focusing on those histologic elements.

Analysis of a pre-2017 follicular variant papillary thyroid carcinoma cohort reclassified as noninvasive follicular thyroid neoplasm with papillary-like features (NIFTP): an 11-year retrospective single institution experience

INTRODUCTION

Noninvasive follicular thyroid neoplasm with papillary-like features (NIFTP), represents a distinct class of thyroid neoplasms with very low risk of adverse outcome and a set of strict histologic criteria. Introduction of NIFTP as a non-cancer has had an appreciable decrease in risk of malignancy and body of literature on this entity continues to grow. In this study, we reviewed clinical, fine-needle aspiration cytology (FNAC), imaging, and molecular findings of histologically proven NIFTPs at our institution.

MATERIALS AND METHODS

Thyroid resections during an 11-year period, with histologic diagnosis of follicular variant of papillary thyroid carcinoma (FVPTC), were retrospectively reviewed to identify NIFTP. Ultrasonographic appearance, FNA findings, and molecular findings were also reviewed.

RESULTS

Of 244 cases of FVPTC identified, 74 (30%) cases were reclassified as NIFTP. Mean tumor size was 2.5 cm. Of 33 patients with lymph node dissection, none had lymph node metastases. On imaging, 36 NIFTP (49%) showed vascularity, 25 (33%) were isoechoic to hypoechoic, there were calcifications in 14 cases (19%), and 7 cases (9%) showed a hypoechoic rim. Bethesda III/IV was the most common interpretation rendered on FNAC (31%). Seven cases had NRAS mutations and 1 case had BRAF V600E mutation. The remaining cases were either negative for BRAF V600E or had no identifiable molecular alterations.

CONCLUSIONS

A significant percentage of tumors previously diagnosed as FVPTC were reclassified as NIFTP. This tumor cannot be reliably diagnosed preoperatively on FNAC, shows no characteristic features on ultrasound and has low suspicion of malignancy. BRAF V600E mutations are infrequent in NIFTP.

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.

Spatially Resolved Molecular Approaches for the Characterisation of Non-Invasive Follicular Tumours with Papillary-like Features (NIFTPs)

Noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) are low-risk thyroid lesions most often characterised by RAS-type mutations. The histological diagnosis may be challenging, and even immunohistochemistry and molecular approaches have not yet provided conclusive solutions. This study characterises a set of NIFTPs by Matrix-Assisted Laser Desorption/Ionisation (MALDI)-Mass Spectrometry Imaging (MSI) to highlight the proteomic signatures capable of overcoming histological challenges. Archived formalin-fixed paraffin-embedded samples from 10 NIFTPs (n = 6 RAS-mutated and n = 4 RAS-wild type) were trypsin-digested and analysed by MALDI-MSI, comparing their profiles to normal tissue and synchronous benign nodules. This allowed the definition of a four-peptide signature able to distinguish RAS-mutant from wild-type cases, the latter showing proteomic similarities to hyperplastic nodules. Moreover, among the differentially expressed signals, Peptidylprolyl Isomerase A (PPIA, 1505.8 m/z), which has already demonstrated a role in the development of cancer, was found overexpressed in NIFTP RAS-mutated nodules compared to wild-type lesions. These results underlined that high-throughput proteomic approaches may add a further level of biological comprehension for NIFTPs. In the future, thanks to the powerful single-cell detail achieved by new instruments, the complementary NGS-MALDI imaging sequence might be the correct methodological approach to confirm that the current NIFTP definition encompasses heterogeneous lesions that must be further characterised.

A new paradigm for epidermal growth factor receptor expression exists in PTC and NIFTP regulated by microRNAs

Intoduction

Identification of molecular alterations associated with tumor behavior is necessary to guide clinical management. The 2022 WHO classification has organized the thyroid follicular cell-derived neoplasms into benign, low-risk and high-risk neoplasms, and emphasized the value of biomarkers that may provide differential diagnostic and prognostic information to avoid overtreatment of low risk neoplasms. This work aims to study the epidermal growth factor receptor (EGFR) expression, functional and spatial dynamics in relation to specific miRNAs alterations in papillary thyroid cancer (PTC) and in non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) considered as models of high-risk and low-risk thyroid tumors respectively.

Methods

Primary thyroid cultured cells were used for miRNA gain/loss of function and luciferase reporter assays. Paraffin embedded tissues were used for real time PCR, immuno-fluorescence stain and confocal microscopy experiments.

Results

Our results showed that in PTC, EGFR mRNA is reduced as an effect of miR-146b-5p upregulation. The EGF expression is low and the ERK pathway is inhibited. The EGFR protein high cytoplasmic expression and colocalization with the endosomal/exosomal markers, ALIX and CD63, suggest the occurrence of stress-induced EGFR internalization, accumulation in endosomal vesicles and secretion via exosomes. In NIFTP EGFR transcription is increased in association with downregulation of miR-7-5p and the EGFR/ERK pathway is active indicating dependence on the canonical EGFR pathway for growth.

Conclusion

Downregulation of transcript level along with cytoplasmic accumulation of undegraded protein is a new pattern of EGFR regulation associated with malignancy in thyroid. Further research is needed to elucidate the intracellular trafficking defects responsible for this specific EGFR dynamic in PTC.

Encapsulated Follicular Variant of Papillary Thyroid Carcinoma: A review on Surgical Treatment

Differentiated thyroid carcinoma is one of the commonest malignancies in head and neck region. Among differentiated thyroid carcinoma, papillary carcinoma is the commonest. Encapsulated follicular variant of papillary thyroid carcinoma tumors are very indolent tumors which behave like benign tumors. Many tumors have been over diagnosed and over treated in spite of their indolent nature. We aimed to find out if total thyroidectomy is really required for very low grade tumors like encapsulated FVPTC. We operated 672 patients of thyroid disease during 2012 to 2020 in SMS Medical College, Jaipur. Out of 256 patients, 199 patients (78%) had papillary carcinoma of thyroid. Classical variant was present in 40% and follicular variant was present in 35% (N-69). Out of 69 patients with follicular variant of PTC, 59 patients had well encapsulated type of follicular variant of PTC while 10 patients had invasive type of follicular variant of PTC. Encapsulated FVPTC are less aggressive and indolent tumors. They should be treated more conservatively. Hemithyroidectomy is sufficient treatment for its complete cure. Out of 69 patients with Follicular variant of PTC, 59 patients had encapsulated disease. Out of 59 patients, 14 (24%) had bilateral nodular disease. 45 (77%) patients had unilateral disease; multicentric in one lobe in 9 (15%) patients and unicentric in 36 (61%) patients. However, encapsulated FVPTC was only found in predominant lobe and the non dominant lobe had benign disease.

Variation in the Diagnosis of Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features

CONTEXT

Noninvasive encapsulated follicular variant of papillary thyroid cancer was reclassified as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) in January 2017. The impact of this nomenclature change at a population level remains unknown.

OBJECTIVE

Examine use of NIFTP across different US regions and populations.

DESIGN

Descriptive epidemiology study using SEER-22 data (2000-2019).

PARTICIPANTS

Individuals diagnosed with papillary or follicular thyroid cancer (2000-2019) or NIFTP (2017-2019).

MAIN OUTCOME MEASURES

Annual incidence rates of thyroid cancer by subtype and NIFTP. Using 2018-2019 data, (1) rates of NIFTP at the 17 SEER-22 sites and (2) comparison of demographics for patients diagnosed with NIFTP vs papillary and follicular thyroid cancer.

RESULTS

NIFTP comprised 2.2% and 2.6% of cases in 2018 and 2019, respectively. Between 2018 and 2019, large heterogeneity was observed in the regional use of NIFTP diagnosis, with site-specific incidence rates between 0.0% and 6.2% (median 2.8%, interquartile range 1.3-3.6%). A diagnosis of NIFTP (vs papillary and follicular thyroid cancer) in 2018 and 2019 was significantly associated with older age (P = 0.012 and P = 0.009, respectively), Black race (both Ps < 0.001), and non-Hispanic ethnicity (both Ps < 0.001).

CONCLUSIONS

Marked variation exists in the use of the NIFTP diagnosis. The recent 2021 coding change that resulted in NIFTP, a tumor with uncertain malignant potential and for which there is no long-term outcome data available, no longer being a reportable diagnosis to SEER will disproportionately affect vulnerable patient groups such as older patients and Black patients, in addition to patients who reside in regions with higher rates of NIFTP diagnoses.

Non-invasive follicular neoplasm with papillary-like nuclear features: a challenging and infrequent entity in Argentina

PURPOSE

Non-invasive encapsulated follicular variant of papillary thyroid cancer was reclassified as non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). These neoplasms have an extremely low malignant potential. The aim of this study was (1) to assess the prevalence of NIFTP in patients with papillary thyroid carcinoma, (2) to evaluate their outcomes, and (3) to determine their molecular profile.

METHODS

Multicenter, descriptive, retrospective study. Patients with papillary thyroid cancer diagnosed from January 2006 to December 2016 from 11 referral centers were included. Diagnosis of NIFTP was based on criteria described by Nikiforov et al. in 2018. At least two pathologists agreed on the diagnosis. Two thousand six hundred and seventy-seven papillary thyroid cancer patients were included; 456 (17%) of them were follicular variant papillary thyroid cancer, and 30 (1.12%) fulfilled diagnostic criteria for NIFTP.

RESULTS

Each of the 30 included patients underwent a total thyroidectomy, and 50% were treated with radioiodine (median dose 100 mCi). After a median follow-up of 37 months, 84% of patients had an excellent response, 3% had an indeterminate response and data was missing in the remaining 13%. No metastatic lymph nodes, distant metastases or recurrences were found. RAS mutations were detected in 4 patients (13%).

CONCLUSION

The prevalence of NIFTP in our series is amongst the lowest reported. Excellent outcomes of patients underscore their low malignant potential. Molecular findings differ from other series, probably related to environmental or ethnic features of our population and the meticulous criteria for diagnosing NIFTP.