NRAS Q61R immunohistochemical staining in thyroid pathology: sensitivity, specificity and utility

Next-Generation Immunohistochemistry in Thyroid Neoplasm: A Practical Review on the Applications in Diagnosis and Molecular Classification

An integrative histologic and molecular classification of thyroid tumors has become clinically relevant due to the potential role in risk stratification and selection of targeted therapy. In this review, we discuss the applications of six "next-generation" immunohistochemical markers, namely BRAF V600E (clone VE1), RAS Q61R (clone SP174), pan-TRK (clone EPR 17341), ALK (clones 5A4 or D5F3), PTEN, and β-catenin in the pathologic diagnosis and molecular classification of thyroid tumors. These biomarkers allow the in situ examination of tumor tissue and assist in the diagnosis and pathologic staging by highlighting tumor border and patterns of invasion, identifying isolated tumor cells in lymph nodes, distinguishing lymph node metastasis from benign intranodal thyroid inclusions, and diagnosing multicentric thyroid carcinomas with discordant molecular drivers. Furthermore, it can identify specific thyroid neoplasms that may occur sporadically or may be associated with hereditary syndromes. The next-generation immunohistochemistry provides a novel solution to challenging issues in thyroid pathology and fast turn-around time for accurate molecular classification and further guidance of therapeutic management.

Diagnostic and Predictive Immunocytochemistry in Head and Neck Lesions

BACKGROUND

The application of immunocytochemistry (ICC) as a diagnostic and predictive tool in the workup of head and neck lesions has followed the changes and progresses in the surgical pathology evaluation. The contribution of ICC has shown a significant role in head and neck cytology, demonstrating as its contribution can support the diagnosis of many lesions. Furthermore, its role has been evolving as an important adjuvant tool in targeted therapies. An additional useful role is defined by the recent introduction of ICC markers related to genetic alterations, which has opened the door to the adoption of a surrogate for molecular evaluation also on cytological material.

SUMMARY

The current review article analyzes the role of ICC in the field of head and neck cytology, showing that it might represent a valid diagnostic tool in difficult cases. The review will include all the different head and neck lesions, demonstrating how we could rely on organ-specific ICC markers but also on ICC markers able to discriminate between benign and malignant lesions.

KEY MESSAGES

The role of ICC represents a valid additional tool in the management of several difficult lesions, especially when morphology alone is not able to make a conclusive diagnosis. The support of ICC is likely to support the morphological findings leading to the definition of the diagnosis and the most appropriate management.

Surgical and Pathological Challenges in Thyroidectomy after Thermal Ablation of Thyroid Nodules

Background: Thermal ablation is a minimally invasive treatment for benign thyroid nodules, but its impact on subsequent thyroidectomy and pathological evaluation is uncertain. This study investigates whether preoperative ablation complicates thyroidectomy and poses challenges for pathological diagnosis. Study Design: This retrospective cohort study used prospectively collected institutional registry data on patients with benign thyroid nodules who underwent thyroidectomy after prior radiofrequency ablation. Perioperative outcomes, including thyroidectomy difficulty scale (TDS) and macroscopic adhesion score (MAS), were compared with a control group without prior ablation. Histopathological and cytological changes within the ablated zone and periphery were also evaluated. Results: This study included 165 patients, with 145 in the nonablation group and 20 in the postablation group (17 females, mean age 53.4 years, mean nodule size 4.4 cm, mean interval between ablation and thyroidectomy 29.5 months). Compared with the nonablation group, the ablation group had longer operative time (99.5 vs. 69.5 minutes, p < 0.05), higher TDS (9 vs. 6, p < 0.05), more severe MAS (anterior 50.0% vs. 16.6%, p < 0.05; posterior: 35.0% vs. 16.6%, p < 0.05), and increased incidental parathyroidectomies (10.7% vs. 1.6%, p < 0.05). Histopathologically, the ablated area showed acellular hyalinization (95%), coagulative necrosis (60%), and chronic inflammation (85%). Both central and peripheral regions displayed cytological alterations (nuclear enlargement, focal chromatin clearing, and clear-cell change). Challenges in defining tumor capsule integrity were noted in eight follicular neoplasms, complicating the diagnosis of three follicular carcinomas and two follicular tumors of uncertain malignant potential. Conclusions: Thermal ablation of thyroid nodules may be associated with increased surgical difficulty and adhesion formation during subsequent thyroidectomy. Additionally, ablation-induced tissue alterations can potentially complicate pathological diagnosis. However, due to the small number of study cases, further confirmatory research is needed.

The Potential Utility of RAS Q61R Immunohistochemistry as a Screening Tool in Pre-operative Fine Needle Aspirates of Medullary Thyroid Carcinoma

Medullary thyroid carcinoma (MTC) can either be sporadic, often via mutually exclusive RET or RAS alterations, or inherited via a RET germline alteration. Germline testing is recommended for all patients diagnosed with MTC. RAS p.Q61R immunohistochemistry (RASQ61R-IHC) can identify a subset of RAS-mutated MTCs on resections, but whether this could be applied pre-operatively to cytology specimens remains unclear. Herein, we assessed RASQ61R-IHC in a tri-institutional cohort of cytologic and histologic MTC specimens with available molecular and germline data. Thirty-four fine needle aspirates with cell blocks were identified between three institutions from 2009 to 2024 with corresponding histology. Tumor sequencing and germline data were recorded, if available. RASQ61R-IHC was scored on staining intensity with documentation of membranous accentuation. Sensitivity, specificity, positive predictive (PPV), and negative predictive values (NPV) were calculated. Of the MTCs, 29% were germline-mutated, and 71% were sporadic. Among all sporadic MTCs (n = 22), 41% were RET-altered, 27% were RAS-altered, and 31.8% did not have available data. With any RASQ61R-IHC staining considered positive, sensitivity, specificity, PPV, and NPV for detecting RAS p.Q61R-mutated MTCs were 100%, 72.7%, 45.4%, and 100%, respectively. Requiring a stain score of > 1 and/or membranous accentuation for a true positive changed sensitivity, specificity, PPV, and NPV to 100%, 100%, 100%, and 100%, respectively. RASQ61R-IHC membranous staining was 100% predictive of RET-negative germline testing. RASQ61R-IHC, when requiring a score > 1 and/or membranous stain accentuation for true positive, had high sensitivity and specificity for RAS p.Q61R mutation in cytologic and surgical MTC specimens. Moreover, RASQ61R-IHC is a rapid and inexpensive modality that could potentially tailor which MTC patients undergo germline testing.

Multidisciplinary Canadian consensus on the multimodal management of high-risk and radioactive iodine-refractory thyroid carcinoma

Most follicular cell-derived differentiated thyroid carcinomas are regarded as low-risk neoplasms prompting conservative therapeutic management. Here, we provide consensus recommendations reached by a multidisciplinary group of endocrinologists, medical oncologists, pathologists, radiation oncology specialists, a surgeon and a medication reimbursement specialist, addressing more challenging forms of this malignancy, focused on radioactive iodine (RAI)-resistant or -refractory differentiated thyroid carcinoma (RAIRTC). In this document we highlight clinical, radiographic, and molecular features providing the basis for these management plans. We distinguish differentiated thyroid cancers associated with more aggressive behavior from thyroid cancers manifesting as poorly differentiated and/or anaplastic carcinomas. Treatment algorithms based on risk-benefit assessments of different multimodal therapy approaches are also discussed. Given the scarcity of data supporting management of this rare yet aggressive disease entity, these consensus recommendations provide much needed guidance for multidisciplinary teams to optimally manage RAIRTC.

Aggressive Types of Malignant Thyroid Neoplasms

Differentiated thyroid cancer (DTC) includes many subtypes, which demonstrate favorable to aggressive behavior. During the past decades, efforts have been made to describe aggressive thyroid cancers. Within DTC, aggressive variants constitute rare entities with unique histopathological features and compromised survival, as local and distant metastatic disease is frequent. In recent years, the distinct category of poorly differentiated thyroid cancer was introduced in 2004 and the type of differentiated high-grade thyroid carcinoma was recently added in the 2022 WHO classification of thyroid neoplasms. Finally, anaplastic thyroid cancer exhibits a rapid, resistant to therapy, progression and confers the shortest survival. In this review, we will present the characteristics of these thyroid cancer types and also discuss the treatment, management, and follow-up of these difficult cases. Emphasis was given to recent bibliography of the last decade.

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.

Detection of RAS p.Q61R by Immunohistochemistry in Practice: A Clinicopathologic Study of 217 Thyroid Nodules with Molecular Correlates

RAS p.Q61R is the most prevalent hot-spot mutation in RAS and RAS-like mutated thyroid nodules. A few studies evaluated RAS p.Q61R by immunohistochemistry (RASQ61R-IHC). We performed a retrospective study of an institutional cohort of 150 patients with 217 thyroid lesions tested for RASQ61R-IHC, including clinical, cytologic and molecular data. RASQ61R-IHC was performed on 217 nodules (18% positive, 80% negative, and 2% equivocal). RAS p.Q61R was identified in 76% (n = 42), followed by RAS p.Q61K (15%; n = 8), and RAS p.G13R (5%; n = 3). NRAS p.Q61R isoform was the most common (44%; n = 15), followed by NRAS p.Q61K (17%; n = 6), KRAS p.Q61R (12%; n = 4), HRAS p.Q61R (12%; n = 4), HRAS p.Q61K (6%; n = 2), HRAS p.G13R (6%; n = 2), and NRAS p.G13R (3%; n = 1). RASQ61R-IHC was positive in 47% of noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP; 17/36), 22% of follicular thyroid carcinomas (FTC; 5/23), 10% of follicular thyroid adenomas (FTA; 4/40), and 8% of papillary thyroid carcinomas (PTC; 9/112). Of PTC studied (n = 112), invasive encapsulated follicular variant (IEFVPTC; n = 16) was the only subtype with positive RASQ61R-IHC (56%; 9/16). Overall, 31% of RAS-mutated nodules were carcinomas (17/54); and of the carcinomas, 94% (16/17) were low-risk per American Thyroid Associated (ATA) criteria, with only a single case (6%; 1/17) considered ATA high-risk. No RAS-mutated tumors recurred, and none showed local or distant metastasis (with a follow-up of 0-10 months). We found that most RAS-mutated tumors are low-grade neoplasms. RASQ61R-IHC is a quick, cost-effective, and reliable way to detect RAS p.Q61R in follicular-patterned thyroid neoplasia and, when malignant, guide surveillance.

Divergent Lineage Markers in Anaplastic Thyroid Carcinoma

Anaplastic thyroid carcinoma (ATC) often results from dedifferentiation of differentiated thyroid carcinoma (DTC), and the diagnosis is not difficult, as the tumor is seen to progress from a recognized DTC. However, in some cases, the diagnosis based on biopsy of limited tissue or resection of a completely undifferentiated tumor relies on immunohistochemical biomarkers and is usually a diagnosis of exclusion. To examine the biomarker profile of ATC and to determine whether divergent lineage markers can complicate this process, we examined the expression of a number of biomarkers in a series of ATCs. Cases retrieved from the department laboratory information system were included if there was evidence of an accurate diagnosis based on the presence of a coexisting or antecedent DTC or in cases where the immunoprofile was consistent with thyroid origin in a non-equivocal clinical setting. Questionable cases were excluded. We identified 36 cases for analysis. Tissue sections were stained for PAX8, TTF1, BRAFV600E, NRASQ61R, TRK, and p53, as well as p40, CDX2, SATB2, GATA3, CD117, CD163, SALL4, SMARCA4, PRAME, SOX10, ERG and HEPPAR1. As expected, all 36 ATCs were negative for TTF1 except for one showing focal, weak expression. Thirteen expressed PAX8 with variable intensity. BRAFV600E was positive in 10/34 tumors and equivocal in 3; NRASQ61R was positive in 12, and TRK was positive in 1 case. Staining for p53 was diffusely positive in 14 and completely negative in 19, with only 3 cases showing a wild-type pattern. We found aberrant expression of GATA3 in 11/36 cases, SATB2 in 8/36, CD117 in 2/35, and SALL4 in 1/30. CD163 expression was identified in tumor cells in 10/30 cases with variable intensity; in the other tumors, interpretation was obscured by abundant histiocytes. P40 was positive in 5 cases with squamoid morphology. CDX2 was negative in 35 tested cases. PRAME was identified in 1 of 33 cases. Stains for SOX10, ERG, and HEPPAR1 were negative in 33 cases. Twenty tested cases showed retained SMARCA4 expression. We conclude that ATCs express a number of divergent lineage markers that can cause diagnostic dilemmas, as they are also features of other tumors in the differential diagnosis of high-grade midline neck malignancies.

Reevaluating diagnostic categories and associated malignancy risks in thyroid core needle biopsy

As the application of core needle biopsy (CNB) in evaluating thyroid nodules rises in clinical practice, the 2023 Korean Thyroid Association Management Guidelines for Patients with Thyroid Nodules have officially recognized its value for the first time. CNB procures tissue samples preserving both histologic structure and cytologic detail, thereby supplying substantial material for an accurate diagnosis and reducing the necessity for repeated biopsies or subsequent surgical interventions. The current review introduces the risk of malignancy within distinct diagnostic categories, emphasizing the implications of noninvasive follicular thyroid neoplasm with papillary-like nuclear features on these malignancy risks. Prior research has indicated diagnostic challenges associated with follicular-patterned lesions, resulting in notable variation within indeterminate diagnostic categories. The utilization of mutation-specific immunostaining in CNB enhances the accuracy of lesion classification. This review underlines the essential role of a multidisciplinary approach in diagnosing follicular-patterned lesions and the potential of mutation-specific immunostaining to strengthen diagnostic consensus and inform patient management decisions.

Preoperative Risk Stratification of Follicular-patterned Thyroid Lesions on Core Needle Biopsy by Histologic Subtyping and RAS Variant-specific Immunohistochemistry

Follicular-patterned lesions often have indeterminate results (diagnostic category III or IV) by core needle biopsy (CNB) and fine needle aspiration (FNA). However, CNB diagnoses follicular neoplasm (category IV) more frequently than FNA. Therefore, we aimed to develop a risk stratification system for CNB samples with category III/IV using immunohistochemistry (IHC). The specificity of the RAS Q61R antibody was validated on 58 thyroid nodules with six different types of RAS genetic variants and 40 cases of RAS wild-type. We then applied IHC analysis of RAS Q61R to 207 CNB samples with category III/IV in which all patients underwent surgical resection. RAS Q61R IHC had 98% sensitivity and 98% specificity for detecting the RAS p.Q16R variant. In an independent dataset, the positive rate of RAS Q61R was significantly higher in NIFTP (48%) and malignancies (45%) than in benign tumors (19%). The risk of NIFTP/malignancy was highest in the group with nuclear atypia and RAS Q61R expression (86%) and lowest in the group without both parameters (32%). The high-risk group with either nuclear atypia or RAS Q61R had 67.3% sensitivity, 73.4% specificity, 75.2% positive predictive value, and 65.1% negative predictive value for identifying NIFTP/malignancy. We conclude that RAS Q61R IHC can be a rule-in diagnostic test for NIFTP/malignancy in CNB category III/IV results. Combining of the histologic parameter (nuclear atypia) with RAS Q61R IHC results can further stratify CNB category III/IV into a high-risk group, which is sufficient for a surgical referral, and a low-risk group sufficient for observation.

This is Your Thyroid on Drugs: Targetable Mutations and Fusions in Thyroid Carcinoma

This review aims to provide an overview of the molecular pathogenesis thyroid carcinomas, emphasizing genetic alterations that are therapeutically actionable. The main pathways in thyroid carcinogenesis are the MAPK and PI3K pathways. Point mutations and gene rearrangements affecting the pathway effectors and receptor tyrosine kinases are well-known drivers of thyroid cancer. Research over the past few decades has successfully introduced highly effective treatments for unresectable thyroid cancer, evolving from multi-kinase inhibitors to structurally selective agents, with constantly improving toxicity profiles and coverage of resistance mechanisms. The pros and cons of major laboratory techniques for therapeutic target identification are discussed.

High-Grade Non-Anaplastic Thyroid Carcinomas of Follicular Cell Origin: A Review of Poorly Differentiated and High-Grade Differentiated Carcinomas

Poorly differentiated thyroid carcinoma (PDTC) and high-grade differentiated thyroid carcinoma (HGDTC) are considered high-grade follicular-derived thyroid carcinomas, with prognoses intermediate between well-differentiated and anaplastic thyroid carcinoma. Both share the presence of invasion, thyroid follicular-cell origin, and tumor necrosis or increased mitoses (≥ 3 mitoses per 2 mm² in PDTC and ≥ 5 mitoses per 2 mm² in HGDTC), without anaplastic dedifferentiation. PDTC must possess solid, trabecular, or insular growth and lack classic papillary-like nuclei; HGDTC can be of any architectural or nuclear morphology (follicular-like, papillary-like, oncocytic). Transformation may be accompanied by acquisition of high-risk mutations (such as TP53 or TERT promoter) on top of RAS-like or BRAF p.V600E-like (including NTRK-fusion) initial driver mutations. These carcinomas most frequently affect adults and often present with metastases (20-50%) or wide local invasion. As PDTC and HGDTC may be radioactive iodine resistant, post-surgical therapy may consist of external beam radiotherapy or targeted, mutation-dependent chemotherapy, such as tyrosine kinase inhibitors. Ten-year disease specific survival is as low as 50%. Awareness of high-grade features in the diagnostic setting is important for patient prognosis and triage of tissue for molecular analysis in order to guide relevant clinical management and therapy.

NRAS Gene Mutation in Differentiated High-Grade Thyroid Carcinoma With Multiphenotypic Metastatic Pattern: A Case Report

Differentiated high-grade thyroid carcinoma (DHGTC) has a high mitotic count (≥5 mitoses per 2mm²) and/or tumor necrosis without anaplastic features. These tumors are rare, and the prevalence is not yet established among thyroid malignancies. BRAF andRAS mutations are the main driver mutations in these tumors. We present a case of a 43-year-old woman with DHGTC and NRASmutation, presenting with metastatic follicular component to the bone and papillary component to lymph nodes.

Redefining the Solid Variant of Papillary Thyroid Carcinoma: A Multi-institutional Retrospective Study

AIMS

The definition of papillary thyroid carcinoma, solid variant (PTC-SV) varies from >50% to 100% of solid/trabecular/insular growth (STI). We aimed to identify prognostic factors and to establish an appropriate STI cutoff for PTC-SV in this multi-institutional study of 156 PTCs with STI.

RESULTS

Nodal metastases were seen in 18% and were associated with higher percentage of papillary and STI. When substratified by infiltration/encapsulation status, STI percentage did not impact risk of nodal metastasis. pN1 stage was seen in 51% of infiltrative tumors and 1% of encapsulated lesions. Overall, PTC with STI had an excellent prognosis. The 10-year DFS was 87% in the entire cohort, 94% in encapsulated lesions, and 76% in infiltrative tumors. STI percentage did not impact DFS. Fifty-four patients had noninvasive encapsulated lesions with 2% to 100% STI. None developed recurrence. Encapsulated lesions were enriched with RAS mutations (54%), whereas infiltrative lesions lacked RAS mutations (4%). BRAF V600E mutation was an infrequent event, being seen in 11% of the entire cohort.

CONCLUSION

In PTC with STI, the determining factor for nodal metastasis and DFS is the encapsulation/infiltration status rather than STI percentage. Encapsulated noninvasive tumors with STI follow an indolent course with a very low risk of nodal metastasis and recurrence. Overall, PTC with STI has an excellent prognosis with a 10-year DSS and DFS of 96% and 87% respectively. Therefore, the classification of SV-PTC as an aggressive PTC subtype may be reconsidered.