The Presence of Typical "BRAFV600E-Like" Atypia in Papillary Thyroid Carcinoma is Highly Specific for the Presence of the BRAFV600E Mutation

Clinicopathological analysis of thyroid carcinomas with the RET and NTRK fusion genes: characterization for genetic analysis

Thyroid carcinomas exhibit various genetic alterations, including the RET and NTRK fusion genes that are targets for molecular therapies. Thus, detecting fusion genes is crucial for devising effective treatment plans. This study characterized the pathological findings associated with these genes to identify the specimens suitable for genetic analysis. Thyroid carcinoma cases positive for the fusion genes were analyzed using the Oncomine Dx Target Test. Clinicopathological data were collected and assessed. Among the 74 patients tested, 8 had RET and 1 had NTRK3 fusion gene. Specifically, of the RET fusion gene cases, 6 exhibited "BRAF-like" atypia and 2 showed "RAS-like" atypia, while the single case with an NTRK3 fusion gene presented "RAS-like" atypia. Apart from one poorly differentiated thyroid carcinoma, most cases involved papillary thyroid carcinomas (PTCs). Primary tumors showed varied structural patterns and exhibited a high proportion of non-papillary structures. Dysmorphic clear cells were frequently observed. BRAF V600E immunoreactivity was negative in all cases. Interestingly, some cases exhibited similarities to diffuse sclerosing variant of PTC characteristics. While calcification in lymph node metastases was mild, primary tumors typically required hydrochloric acid-based decalcification for tissue preparation. This study highlights the benefits of combining morphological and immunohistochemical analyses for gene detection and posits that lymph node metastases are more suitable for genetic analysis owing to their mild calcification. Our results emphasize the importance of accurate sample processing in diagnosing and treating thyroid carcinomas.

The road ahead: a brief guide to navigating the 2022 WHO classification of endocrine and neuroendocrine tumours

The most recent WHO classification of endocrine and neuroendocrine tumours has brought about significant changes in the diagnosis and grading of these lesions. For instance, pathologists now have the ability to stratify subsets of thyroid and adrenal neoplasms using various histological features and composite risk assessment models. Moreover, novel recommendations on how to approach endocrine neoplasia involve additional immunohistochemical analyses, and the recognition and implementation of these key markers is essential for modernising diagnostic capabilities. Additionally, an improved understanding of tumour origin has led to the renaming of several entities, resulting in the emergence of terminology not yet universally recognised. The adjustments in nomenclature and prognostication may pose a challenge for the clinical team, and care providers might be eager to engage in a dialogue with the diagnosing pathologist, as treatment guidelines have not fully caught up with these recent changes. Therefore, it is crucial for a surgical pathologist to be aware of the knowledge behind the implementation of changes in the WHO classification scheme. This review article will delve into the most significant diagnostic and prognostic changes related to lesions in the parathyroid, thyroid, adrenal glands and the gastroenteropancreatic neuroendocrine system. Additionally, the author will briefly share his personal reflections on the clinical implementation, drawing from a couple of years of experience with these new algorithms.

Are there specific cytologic features that can predict BRAFV600E mutational status of papillary thyroid carcinoma in fine-needle aspiration specimens?

BACKGROUND

BRAFV600E mutation is the most common molecular alteration found in papillary thyroid carcinoma (PTC) and has been linked to recurrent disease or possibly more aggressive behavior. Some studies have reported sickle-shaped nuclei (SSN) and plump pink cells (PPC) to be predictive markers of BRAF mutation in FNA cytology. We aimed to evaluate the reproducibility of the aforementioned cytologic features.

METHODS

A computerized search for diagnosed PTC surgical pathology cases tested for BRAFV600E mutation by Sanger DNA sequencing was performed. Blinded to BRAF results, the corresponding cytology was reviewed for presence of SSN and PPC. Classic nuclear PTC (CNPTC) features, cystic change, and psammoma bodies were also evaluated. The results were correlated with BRAFV600E mutational status and histologic subtypes.

RESULTS

Study cohort consisted of 113 cases (74 BRAFV600E mutated, 39 BRAFV600E wild type). SSN and combined CNPTC /SSN had positive predictive value of 74% and 75%, respectively. CNPTC showed 92% sensitivity and 20% specificity. Psammoma bodies had 92% specificity and 5% sensitivity. The presence of combined PPC/SSN showed 80% specificity, 27% sensitivity, and diagnostic accuracy of 45%. CNPTC was seen in 60/61 (98%) SSN and 45/45 (100%) PPC. There was no significant statistical association between SSN, PPC, and CNPTC with specific histologic subtypes and BRAF mutational status.

CONCLUSION

CNPTC is sensitive but not specific for BRAF mutational status. SSN, PPC, and CNPTC are not predictive markers for the presence of BRAF mutation or histologic subtypes. Additional studies may be needed to further corroborate these findings.

Clinicopathologic Features and Cytologic Correlation of ALK-Rearranged Papillary Thyroid Carcinoma: A Series of Eight Cases

Anaplastic lymphoma kinase (ALK) gene fusions are rare in papillary thyroid carcinoma (PTC) but may serve as a therapeutic target. This study aims to evaluate the preoperative cytologic findings and clinicopathologic features of a series of eight ALK-rearranged PTCs from our pathology archives and consultations. All cases were confirmed by ALK D5F3 immunohistochemistry and six with additional targeted RNA-based next-generation sequencing (NGS). The original fine-needle aspiration (FNA) cytology diagnosis included the Bethesda System (TBS) category II in three (37.5%), TBS III in two (25%), TBS V in two (25%), and TBS VI in one (12.5%). Six cases had available FNA cytology and were reviewed. The cytologic features showed microfollicular architecture as well as limited or reduced nuclear elongation and chromatin alterations in all six. Nuclear grooves and pseudoinclusions were absent in two cases, rarely or focally noted in three, and frequently found in one. Two cases initially diagnosed as TBS II, showing microfollicular architecture without well-developed nuclear features, were revised to TBS III (with architectural atypia only). For histologic correlations, four were infiltrative follicular variant PTCs, three as classic subtype PTC with predominant follicular growth, and one as solid/trabecular subtype PTC. All eight cases demonstrated reduced PTC nuclear features with respect to nuclear elongation and chromatin alterations compared to those typically identified in "BRAF-like" PTCs. The NGS testing revealed EML4::ALK fusion in three, STRN::ALK fusion in two, and ITSN2::ALK fusion in one. In conclusion, although ALK-rearranged PTCs have been associated with neutral gene expression profile from a BRAF-RAS scoring perspective, the "RAS-like" nuclear features were more commonly identified in this series, resulting in frequent indeterminate diagnosis of preoperative FNA.

Differentiating BRAF V600E- and RAS-like alterations in encapsulated follicular patterned tumors through histologic features: a validation study

Differentiating BRAF V600E- and RAS-altered encapsulated follicular-patterned thyroid tumors based on morphology remains challenging. This study aimed to validate an 8-score scale nuclear scoring system and investigate the importance of nuclear pseudoinclusions (NPIs) in aiding this differentiation. A cohort of 44 encapsulated follicular-patterned tumors with varying degrees of nuclear atypia and confirmed BRAF V600E or RAS alterations was studied. Nuclear parameters (area, diameter, and optical density) were analyzed using a deep learning model. Twelve pathologists from eight Asian countries visually assessed 22 cases after excluding the cases with any papillae. Eight nuclear features were applied, yielding a semi-quantitative score from 0 to 24. A threshold score of 14 was used to distinguish between RAS- and BRAF V600E-altered tumors. BRAF V600E-altered tumors typically demonstrated higher nuclear scores and notable morphometric alterations. Specifically, the nuclear area and diameter were significantly larger, and nuclear optical density was much lower compared to RAS-altered tumors. Observer accuracy varied, with two pathologists correctly identifying genotype of all cases. Observers were categorized into proficiency groups, with the highest group maintaining consistent accuracy across both evaluation methods. The lower group showed a significant improvement in accuracy upon utilizing the 8-score scale nuclear scoring system, with notably increased sensitivity and negative predictive value in BRAF V600E tumor detection. BRAF V600E-altered tumors had higher median total nuclear scores. Detailed reevaluation revealed NPIs in all BRAF V600E-altered cases, but in only 2 of 14 RAS-altered cases. These results could significantly assist pathologists, particularly those not specializing in thyroid pathology, in making a more accurate diagnosis.

A Detailed Histologic and Molecular Assessment of the Diffuse Sclerosing Variant of Papillary Thyroid Carcinoma

Diffuse sclerosing variant papillary thyroid carcinoma (DS-PTC) is characterized clinically by a predilection for children and young adults, bulky neck nodes, and pulmonary metastases. Previous studies have suggested infrequent BRAFV600E mutation but common RET gene rearrangements. Using strict criteria, we studied 43 DS-PTCs (1.9% of unselected PTCs in our unit). Seventy-nine percent harbored pathogenic gene rearrangements involving RET, NTRK3, NTRK1, ALK, or BRAF; with the remainder driven by BRAFV600E mutations. All 10 pediatric cases were all gene rearranged (P = .02). Compared with BRAFV600E-mutated tumors, gene rearrangement was characterized by psammoma bodies involving the entire lobe (P = .038), follicular predominant or mixed follicular architecture (P = .003), pulmonary metastases (24% vs none, P = .04), and absent classical, so-called "BRAF-like" atypia (P = .014). There was no correlation between the presence of gene rearrangement and recurrence-free survival. Features associated with persistent/recurrent disease included pediatric population (P = .030), gene-rearranged tumors (P = .020), microscopic extrathyroidal extension (P = .009), metastases at presentation (P = .007), and stage II disease (P = .015). We conclude that DS-PTC represents 1.9% of papillary thyroid carcinomas and that actionable gene rearrangements are extremely common in DS-PTC. DS-PTC can be divided into 2 distinct molecular subtypes and all BRAFV600E-negative tumors (1.5% of papillary thyroid carcinomas) are driven by potentially actionable oncogenic fusions.

A Critical Assessment of Diagnostic Criteria for the Tall Cell Subtype of Papillary Thyroid Carcinoma-How Much? How Tall? And When Is It Relevant?

Tall cell papillary thyroid carcinoma (TC-PTC) is considered adverse histology. However, previous studies are confounded by inconsistent criteria and strong associations with other adverse features. It is therefore still unclear if TC-PTC represents an independent prognostic factor in multivariate analysis and, if it does, what criteria should be employed for the diagnosis. We retrospectively reviewed 487 PTCs from our institution (where we have historically avoided the prospective diagnosis of TC-PTC) for both the height of tall cells (that is if the cells were two, or three, times as tall as wide) and the percentage of tall cells. On univariate analysis, there was significantly better disease free survival (DFS) in PTCs with no significant tall cell component (< 30%) compared to PTCs with cells two times tall as wide (p = 0.005). The proportion of tall cells (30-50% and > 50%) was significantly associated with DFS (p = 0.012). In a multivariate model including age, size, vascular space invasion, and lymph node metastasis, the current WHO tall cell criteria, met by 7.8% of PTCs, lacked statistical significance for DFS (p = 0.519). However, in the subset of tumours otherwise similar to the American Thyroid Association (ATA) guidelines low-risk category, WHO TC-PTC demonstrated a highly significant reduction in DFS (p = 0.004). In contrast, in intermediate to high-risk tumours, TC-PTC by WHO criteria lacked statistical significance (p = 0.384). We conclude that it may be simplistic to think of tall cell features as being present or absent, as both the height of the cells (two times versus three times) and the percentage of cells that are tall have different clinical significances in different contexts. Most importantly, the primary clinical significance of TC-PTC is restricted to PTCs that are otherwise low risk by ATA guidelines.

Association of DNA Promoter Methylation and BRAF Mutation in Thyroid Cancer

The BRAF V600E mutation and DNA promoter methylation play important roles in the pathogenesis of thyroid cancer (TC). However, the association of these genetic and epigenetic alterations is not clear. In this study, using paired tumor and surrounding normal tissue from the same patients, on a genome-wide scale we tried to identify (a) any association between BRAF mutation and DNA promoter methylation, and (b) if the molecular findings may provide a basis for therapeutic intervention. We included 40 patients with TC (female = 28, male = 12) without distant metastasis. BRAF mutation was present in 18 cases. We identified groups of differentially methylated loci (DML) that are found in (a) both BRAF mutant and wild type, (b) only in BRAF mutant tumors, and (c) only in BRAF wild type. BRAF mutation-specific promoter loci were more frequently hypomethylated, whereas BRAF wild-type-specific loci were more frequently hypermethylated. Common DML were enriched in cancer-related pathways, including the mismatch repair pathway and Wnt-signaling pathway. Wild-type-specific DML were enriched in RAS signaling. Methylation status of checkpoint signaling genes, as well as the T-cell inflamed genes, indicated an opportunity for the potential use of PDL1 inhibitors in BRAF mutant TC. Our study shows an association between BRAF mutation and methylation in TC that may have biological significance.