Mutational profile of papillary thyroid microcarcinoma with extensive lymph node metastasis

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.

Comprehensive Long-Read Sequencing Analysis Discloses the Transcriptome Features of Papillary Thyroid Microcarcinoma

CONTEXT

Papillary thyroid microcarcinoma (PTMC) is the most common type of thyroid cancer. It has been shown that lymph node metastasis is associated with poor prognosis in patients with PTMC.

OBJECTIVE

We aim to characterize the PTMC transcriptome landscape and identify the candidate transcripts that are associated with lateral neck lymph node metastasis of PTMC.

METHODS

We performed full-length transcriptome sequencing in 64 PTMC samples. Standard bioinformatic pipelines were applied to characterize and annotate the full-length expression profiles of 2 PTMC subtypes. Functional open reading frame (ORF) annotation of the known and novel transcripts were predicted by HMMER, DeepLoc, and DeepTMHMM tools. Candidate transcripts associated with the pN1b subtype were identified after transcript quantification and differential gene expression analyses.

RESULTS

We found that skipping exons accounted for the more than 27.82% of the alternative splicing events. At least 42.56% of the discovered transcripts were novel isoforms of annotated genes. A total of 39 193 ORFs in novel transcripts and 18 596 ORFs in known transcripts were identified. Distribution patterns of the characterized transcripts in functional domain, subcellular localization, and transmembrane structure were predicted. In total, 1033 and 1204 differentially expressed genes were identified in the pN0 and pN1b groups, respectively. Moreover, novel isoforms of FRMD3, NOD1, and SHROOM4 were highlighted for their association with pN1b subtype.

CONCLUSION

Our data provided the global transcriptome landscape of PTMC and also revealed the novel isoforms that associated with PTMC aggressiveness.

TERT RNAscope analysis of sub-centimetric papillary thyroid carcinomas and synchronous lymph node metastases

BACKGROUND

Sub-centrimetric papillary thyroid carcinomas usually have a good prognosis with a cancer specific survival of > 99%, however in up to 65% of patients, lymph node metastases can be observed. Molecular alterations in BRAF, TERT and TP53 are associated with worse clinicopathological outcome in patients with papillary thyroid carcinoma.

MATERIAL AND METHODS

Twenty-two cases of papillary thyroid carcinomas measuring ≤ 1 cm with synchronous lymph node metastases were examined regarding morphological patterns and immunohistochemical status of p53, Ki-67, and BRAF V600E status. TERT RNA expression in lymph node metastases were evaluated by RNAScope®.

RESULTS

Morphological patterns were heterogeneous in both primary tumors and lymph node metastases. Proliferation indices measured by Ki-67 were low. Both primary and lymph node metastases were wild type for p53 by immunohistochemical analysis. No lymph node metastasis showed TERT expression by RNAScope®.

CONCLUSIONS

Our data indicate that TERT expression is not involved in the development early lymph node metastasis in patients with sub-centimetric PTC.

Circular RNAs: characteristics, functions, mechanisms, and potential applications in thyroid cancer

Thyroid cancer (TC) is one of the most common endocrine malignancies, and its incidence has increased globally. Despite extensive research, the underlying molecular mechanisms of TC remain partially understood, warranting continued exploration of molecular markers for diagnostic and prognostic applications. Circular RNAs (circRNAs) have recently garnered significant attention owing to their distinct roles in cancers. This review article introduced the classification and biological functions of circRNAs and summarized their potential as diagnostic and prognostic markers in TC. Further, the interplay of circRNAs with PI3K/Akt/mTOR, Wnt/β-catenin, MAPK/ERK, Notch, JAK/STAT, and AMPK pathways is elaborated upon. The article culminates with an examination of circRNA's role in drug resistance of TC and highlights the challenges in circRNA research in TC.

Clinicopathological Features and Molecular Signatures of Lateral Neck Lymph Node Metastasis in Papillary Thyroid Microcarcinoma

BACKGRUOUND

The predictive factors for lateral neck lymph node metastasis (LLNM) in papillary thyroid microcarcinoma (PTMC) remain undetermined. This study investigated the clinicopathological characteristics, transcriptomes, and tumor microenvironment in PTMC according to the LLNM status. We aimed to identify the biomarkers associated with LLNM development.

METHODS

We retrospectively reviewed the medical records of patients with PTMC from two independent institutions between 2018 and 2022 (n=597 and n=467). We compared clinicopathological features between patients without lymph node metastasis (N0) and those with LLNM (N1b). Additionally, laser capture microdissection and RNA sequencing were performed on primary tumors from both groups, including metastatic lymph nodes from the N1b group (n=30; 20 primary tumors and 10 paired LLNMs). We corroborated the findings using RNA sequencing data from 16 BRAF-like PTMCs from The Cancer Genome Atlas. Transcriptomic analyses were validated by immunohistochemical staining.

RESULTS

Clinicopathological characteristics, such as male sex, multifocality, extrathyroidal extension, lymphatic invasion, and central node metastasis showed associations with LLNM in PTMCs. Transcriptomic profiles between the N0 and N1b PTMC groups were similar. However, tumor microenvironment deconvolution from RNA sequencing and immunohistochemistry revealed an increased abundance of tumor-associated macrophages, particularly M2 macrophages, in the N1b group.

CONCLUSION

Patients with PTMC who have a male sex, multifocality, extrathyroidal extension, lymphatic invasion, and central node metastasis exhibited an elevated risk for LLNM. Furthermore, infiltration of M2 macrophages in the tumor microenvironment potentially supports tumor progression and LLNM in PTMCs.

Characteristics and risk factors of cervical lymph node metastasis in cN0 papillary thyroid microcarcinoma of the isthmus

The surgical resection range of papillary thyroid microcarcinoma of the isthmus (PTMCI) is controversial, and the guidelines do not fully guide the central lymph node dissection (CLND).We retrospectively studied the comparison of PTMCI (Group A, n = 65 cases) and non-PTMCI (Group B, n = 80 cases). Based on whether central lymph node metastasis (CLNM) was further detected, they were further divided into the PTMCI with CLNM (group C, n = 42 cases), the PTMCI without CLNM (group D, n = 23 cases), the non-PTMCI with CLNM (group E, n = 45 cases), the non-PTMCI without CLNM (group F, n = 35 cases). All patients underwent total thyroidectomy and CLND. The CLNM pathological examination was divided into right recurrent laryngeal nerve superficial lymph nodes (Right VI a), right recurrent laryngeal nerve deep lymph nodes (Right VI b), left VI area lymph nodes (Left VI), prelaryngeal lymph node, and pretracheal lymph node. The extent of lymph node metastasis and risk factors of PTMCI were analyzed by univariate and multivariate analysis. The ROC curve was used to calculate the maximum diameter of the tumor and the Youden index was calculated to analyze the impact of diameter on the risk factors for CLNM in PTMCI. To construct a prediction model of transfer risk of high risk factors by Nomogram, there were significant differences in prelaryngeal lymph nodes (p = 0.034) and pretracheal lymph nodes ( n = 0.035) between group A and group B, and the risk factors of lymph node metastasis were tumor invasion (p = 0.003), multifocality (p = 0.001), and the maximum tumor diameter≧6.5 mm. PTMCI is more prone to metastasis of pretracheal lymph nodes and prelaryngeal lymph nodes, and the presence of tumor invasion, multifocality, and tumor diameter≧6.5 mm are high risk factors for metastasis in PTMCI. According to the prediction model, with all risk factors the risk of cervical lymph node metastasis is up to 90%.

A nomogram based on the risk factors of cervical lymph node metastasis in papillary thyroid carcinoma coexistent with Hashimoto's thyroiditis

OBJECTIVE

The purpose of this study was to explore the risk factors of cervical lymph node metastasis(LNM) in papillary thyroid carcinoma(PTC) coexistent with Hashimoto's thyroiditis(HT).

METHODS

The clinical data of patients who underwent thyroid operation between November 2016 and January 2020 in our hospital were analyzed retrospectively. The association between sonographic features and the risk factors of cervical LNM in PTC coexistent with HT was analyzed and a nomogram based on the risk factors was built.

RESULTS

Age, US features as calcification, blood flow type, distance between thyroid nodule and fibrous capsule were risk factors of cervical LNM(P < 0.05).Size, SWVmax and SWVmean of thyroid nodule, SWVratio between thyroid nodule and thyroid gland were higher in PTCs with LNM than those without LNM(P < 0.05). The ROC curve showed that the cutoff value of SWVratio for predicting LNM was 1.29 (Sensitivity = 0.806, Specificity = 0.775, AUC = 0.823, P < 0.001). Based on the risk factors above, a relevant nomogram prediction model was established. The model verification showed that the C-index of the modeling set was 0.814, indicating that the nomogram model had good predicted accuracy.

CONCLUSION

Based on the risk factors above, a relevant nomogram prediction model was established. The model verification showed that the C-index of the modeling set was 0.814, indicating that the nomogram model had good predicted accuracy. The nomogram based on the risk factors above had good prediction ability, which could optimize thyroidectomy and cervical lymph node dissection and improving prognosis.

Younger Than 55 Years Old and BRAF V600E Mutation are Risk Factors for Lymph Node Metastasis in Papillary Thyroid Carcinomas ≤1.0 cm but Not in >1.0 cm

Background

Studies on the relationship between BRAF V600E mutation and the clinicopathologic features of papillary thyroid carcinoma (PTC), risk of lymph node metastasis in papillary thyroid microcarcinoma (PTMC) have shown inconsistent results.

Methods

In this retrospective analysis, clinicopathological data of the patients were collected, and molecular testing was done for BRAF V600E mutation. PTC patients are divided into PTC≤1.0cm (PTMC) and PTC>1.0cm, and the relationship between BRAF V600E mutation and clinicopathologic features was analyzed respectively.

Results

Of the 520 PTC patients, 432 (83.1%) were female and 416 (80.0%) were <55 years old. BRAF V600E mutation was detected in 422 (81.2%) tumour samples of PTC. There was no significant difference in the frequency of BRAF V600E mutation between different age groups. There were 250 (48.1%) patients with PTMC and 270 (51.9%) patients with PTC>1.0cm. BRAF V600E mutation was significantly associated with bilateral cancer (23.0% vs 4.9%, P=0.005) and lymph node metastasis (61.7% vs 39.0%, P=0.009) in PTMC patients, while BRAF V600E mutation was significantly associated with bilateral cancer (24.9% vs 12.3%, P=0.048) in PTC>1.0cm patients. Logistic regression analysis showed that, after adjusting for gender, Hashimoto's thyroiditis and calcification, we found that younger age (<55 years old) (OR: 2.384, 95% CI: 1.241-4.579, P=0.009) and BRAF V600E mutation (OR: 2.213, 95% CI: 1.085-4.512, P=0.029) were significantly associated with lymph node metastasis in PTMC, similar results were not obtained in PTC>1.0cm.

Conclusion

Younger age (<55 years old) and BRAF V600E mutation was independent risk factor for lymph node metastasis in PTMC.

Male patients with papillary thyroid cancer have a higher risk of extranodal extension

BACKGROUND

There is a sex disparity in papillary thyroid cancer (PTC). Male sex is associated with a higher likelihood of advanced stage disease. This study aimed to examine the significance of sex for extranodal extension (ENE) in PTC.

METHODS

We reviewed the data of PTC patients who had undergone initial surgical resection from July 2012 to December 2014 (N = 1531). The effects of sex and other clinicopathological factors on ENE were investigated.

RESULTS

Of 1531 patients identified, 377 (24.6%) were male, 816 (53.3%) had positive nodes, and 256 (16.7%) had ENE. Compared with female patients, male patients had a higher risk of ENE (P < 0.001). Multivariable analysis of clinicopathological factors revealed that male sex (odds ratio [OR], 1.98; 95% confidence interval [CI], 1.37-2.87; P < 0.001), age older than 60 years (OR, 1.93; 95% CI, 1.08-3.35; P = 0.023), extrathyroidal extension (OR, 3.52; 95% CI, 2.42-5.14; P < 0.001), bilateral multifocality (OR, 2.18; 95% CI, 1.53-3.13; P < 0.001), and more positive nodes were significantly associated with increased risk of ENE. Patients with 6-10 positive nodes were 16.45-fold higher to have ENE than patients with 5 positive nodes or less (95% CI, 11.07-24.68; P < 0.001).

CONCLUSION

Male PTC patients had a higher risk of ENE than female. Sex was an independent predictor of ENE. The underlying mechanism needs to be investigated further.

TERT Promoter Mutations Are an Independent Predictor of Distant Metastasis in Middle Eastern Papillary Thyroid Microcarcinoma

BACKGROUND

Papillary thyroid microcarcinomas (PTMCs) have been attributed to the recent increased incidence of thyroid cancer. Although indolent, a subset of PTMC could potentially develop distant metastasis (DM). This study aimed to evaluate the clinico-pathological features and molecular characteristics of PTMC and identify the risk factors for DM in PTMC patients from Middle Eastern ethnicity.

METHODS

We retrospectively analyzed 210 patients with histologically confirmed PTMC. Clinico-pathological associations for DM, BRAF mutation and TERT mutation were analyzed successfully in 184 patients. Multivariate analysis was performed using Cox proportional hazards model and logistic regression analysis.

RESULTS

Among the PTMC patients included in this cohort, DM was noted in 6.0% (11/184), whereas tumor relapse occurred in 29/184 (15.8%). Of the 11 cases with DM, lung metastasis occurred in 8 cases, bone metastasis in 2 cases and brain metastasis in 1 case. Presence of extrathyroidal extension and male sex were significantly associated with DM. Molecular analysis showed BRAF V600E mutations to be the most frequent, being detected in 45.7% (84/184). TERT promoter mutations were detected in 16 (8.7%) cases and were significantly associated with DM and shorter metastasis-free survival in multivariate analysis.

CONCLUSIONS

Our study indicates a surprisingly high frequency of TERT promoter mutation in Saudi patients with PTMC. Identifying TERT promoter mutations as an independent predictor of DM in patients with microcarcinoma could explain the inherent aggressive nature of PTMC from Middle Eastern ethnicity and magnify its role in patient risk stratification, which might help in improving therapeutic strategy for these patients.

Whole-Exome Sequencing in Papillary Microcarcinoma: Potential Early Biomarkers of Lateral Lymph Node Metastasis

BACKGROUND

Early identification of patients with high-risk papillary thyroid microcarcinoma (PTMC) that is likely to progress has become a critical challenge. We aimed to identify somatic mutations associated with lateral neck lymph node (LN) metastasis (N1b) in patients with PTMC.

METHODS

Whole-exome sequencing (WES) of 14 PTMCs with no LN metastasis (N0) and 13 N1b PTMCs was performed using primary tumors and matched normal thyroid tissues.

RESULTS

The mutational burden was comparable in N0 and N1b tumors, as the median number of mutations was 23 (range, 12 to 46) in N0 and 24 (range, 12 to 50) in N1b PTMC (P=0.918). The most frequent mutations were detected in PGS1, SLC4A8, DAAM2, and HELZ in N1b PTMCs alone, and the K158Q mutation in PGS1 (four patients, Fisher's exact test P=0.041) was significantly enriched in N1b PTMCs. Based on pathway analysis, somatic mutations belonging to the receptor tyrosine kinase-RAS and NOTCH pathways were most frequently affected in N1b PTMCs. We identified four mutations that are predicted to be pathogenic in four genes based on Clinvar and Combined Annotation-Dependent Depletion score: BRAF, USH2A, CFTR, and PHIP. A missense mutation in CFTR and a nonsense mutation in PHIP were detected in N1b PTMCs only, although in one case each. BRAF mutation was detected in both N0 and N1b PTMCs.

CONCLUSION

This first comprehensive WES analysis of the mutational landscape of N0 and N1b PTMCs identified pathogenic genes that affect biological functions associated with the aggressive phenotype of PTMC.

Neo-Fs Index: A Novel Immunohistochemical Biomarker Panel Predicts Survival and Response to Anti-Angiogenetic Agents in Clear Cell Renal Cell Carcinoma

Background: Frameshift indels have emerged as a predictor of immunotherapy response but were not evaluated yet to predict anti-angiogenetic agent (AAA) response or prognosis in clear cell renal cell carcinoma (ccRCC). Methods: Here, to develop biomarkers that predict survival and response to AAA, we evaluated the immunohistochemical expression of proteins whose genes frequently harbor frameshift indels in 638 ccRCC patients and correlated the individual and integrated markers with prognosis and AAA response. The mutational landscape was evaluated using targeted next-generation sequencing in 12 patients concerning protein markers. Immune gene signatures were retrieved from TCGA RNA seq data. Results: Five proteins (APC, NOTCH1, ARID1A, EYS, and filamin A) were independent adverse prognosticators and were incorporated into the Neo-fs index. Better overall, disease-specific and recurrence-free survival were observed with high Neo-fs index in univariate and multivariate survival analyses. Better AAA responses were observed with a high Neo-fs index, which reflected increased MHC class I, CD8+ T cell, cytolytic activity, and plasmacytoid dendritic cell signatures and decreased type II-IFN response signatures, as well as greater single-nucleotide variant (SNV) and indel counts. Conclusions: Neo-fs index, reflecting antitumor immune signature and more SNVs. and indels, is a powerful predictor of survival and AAA response in ccRCC.

The molecular and gene/miRNA expression profiles of radioiodine resistant papillary thyroid cancer

Background

Papillary thyroid cancer (PTC) is the most frequent endocrine tumor. Radioiodine (RAI) treatment is highly effective in these tumors, but up to 60% of metastatic cases become RAI-refractory. Scanty data are available on either the molecular pattern of radioiodine refractory papillary thyroid cancers (PTC) or the mechanisms responsible for RAI resistance.

Methods

We analyzed the molecular profile and gene/miRNA expression in primary PTCs, synchronous and RAI-refractory lymph node metastases (LNMs) in correlation to RAI avidity or refractoriness.

We classified patients as RAI+/D+ (RAI uptake/disease persistence), RAI−/D+ (absent RAI uptake/disease persistence), and RAI+/D- (RAI uptake/disease remission), and analyzed the molecular and gene/miRNA profiles, and the expression of thyroid differentiation (TD) related genes.

Results

A different molecular profile according to the RAI class was observed: BRAF^V600E cases were more frequent in RAI−/D+ (P = 0.032), and fusion genes in RAI+/D+ cases. RAI+/D- patients were less frequently pTERT mutations positive, and more frequently wild type for the tested mutations/fusions. Expression profiles clearly distinguished PTC from normal thyroid. On the other hand, in refractory cases (RAI+/D+ and RAI−/D+) no distinctive PTC expression patterns were associated with either tissue type, or RAI uptake, but with the driving lesion and BRAF−/RAS-like subtype. Primary tumors and RAI-refractory LNMs with BRAF^V600E mutation display transcriptome similarity suggesting that RAI minimally affects the expression profiles of RAI-refractory metastases. Molecular profiles associated with the expression of TPO, SLC26A4 and TD genes, that were found more downregulated in BRAF^V600E than in gene fusions tumors.

Conclusions

The present data indicate a different molecular profile in RAI-avid and RAI-refractory metastatic PTCs. Moreover, BRAF^V600E tumors displayed reduced differentiation and intrinsic RAI refractoriness, while PTCs with fusion oncogenes are RAI-avid but persistent, suggesting different oncogene-driven mechanisms leading to RAI refractoriness.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01757-x.

Prophylactic lymph node dissection in clinically N0 differentiated thyroid carcinoma: example of personalized treatment

Considering the 'differentiated thyroid carcinoma (DTC) epidemic', the indolent nature of DTC imposes a treatment paradigm shift toward elimination of recurrence. Lymph node metastases in cervical compartments, encountered in 20-90% of DTC, are the main culprit of recurrent disease, affecting 5-30% of patients. Personalized risk-stratified cervical prophylactic lymph node dissection (PLND) at initial thyroidectomy in DTC with no clinical, sonographic or intraoperative evidence of lymph node metastases (clinically N0) has been advocated, though not unanimously. The present review dissects the controversy over PLND. Weighing the benefit yielded from PLND up against the PLND-related morbidity is so far hampered by the inconsistent profit yielded by PLND and the challenging patient selection. Advances in tailoring PLND are anticipated to empower optimal patient care.

Low-risk papillary thyroid microcarcinoma: Optimal management toward a more conservative approach

The incidence of papillary thyroid microcarcinoma (microPTC) has dramatically increased in the last decades. Most of these tumors remain small and clinically "silent", only small number progress. Although thyroid surgery used to be the only therapeutic approach, recent guidelines now consider active surveillance for low-risk microPTC. For this reason, more accurate risk stratification of microPTC is needed. The optimal management of low-risk microPTC through accurate risk stratification represents a major clinical issue.

Unmet Clinical Needs in the Treatment of Patients with Thyroid Cancer

The increased incidence of thyroid cancer is a worldwide phenomenon; however, the issue of overdiagnosis has been most prominent in South Korea. The age-standardized mortality rate of thyroid cancer in Korea steeply increased from 1985 to 2004 (from 0.17 per 100,000 to 0.85 per 100,000), and then decreased until 2015 to 0.42 per 100,000, suggesting that early detection reduced mortality. However, early detection of thyroid cancer may be cost-ineffective, considering its very high prevalence and indolent course. Therefore, risk stratification and tailored management are vitally important, but many prognostic markers can only be evaluated postoperatively. Discovery of preoperative marker(s), especially for small cancers, is the most important unmet clinical need for thyroid cancer. Herein, we discuss some such factors that we recently discovered. Another unmet clinical need is better treatment of radioiodine-refractory (RAIR) differentiated thyroid cancer (DTC) and undifferentiated cancers. Although sorafenib and lenvatinib are available, better drugs are needed. We found that phosphoglycerate dehydrogenase, a critical enzyme for serine biosynthesis, could be a novel therapeutic target, and that the lymphocyte-to-monocyte ratio is a prognostic marker of survival in patients with anaplastic thyroid carcinoma or RAIR DTC. Deeper insights are needed into tumor-host interactions in thyroid cancer to improve treatment.

Characterization of thyroid cancer driven by known and novel ALK fusions

ALK fusions are found in various tumors, including thyroid cancer, and serve as a diagnostic marker and therapeutic target. Spectrum and outcomes of ALK fusions found in thyroid nodules and cancer are not fully characterized. We report a series of 44 ALK-translocated thyroid neoplasms, including 31 identified preoperatively in thyroid fine-needle aspirates (FNA). The average patients' age was 43 years (range, 8-76 years); only one with radiation history. All 19 resected thyroid nodules with ALK fusion identified preoperatively were malignant. Among nodules with known surgical pathology (n = 32), 84% were papillary thyroid carcinomas (PTCs) and 16% poorly differentiated thyroid carcinomas (PDTCs). PTCs showed infiltrative growth with follicular architecture seen exclusively (30%) or in combination with papillary and/or solid growth (37%). Tumor multifocality was seen in 10 (31%) PTC cases. Most PDTC had a well-differentiated PTC component. Lymph node metastases were identified in 10/18 (56%) patients with neck dissection. The most common ALK fusion partners were STRN (n = 22) and EML4 (n = 17). In five cases, novel ALK fusion partners were discovered. All five PDTCs carried STRN-ALK fusion. On follow-up, ten patients were free of disease at 2-108 months, whereas two patients with PDTC died of disease. In summary, ALK fusion-positive thyroid carcinomas are typically infiltrative PTC with common follicular growth, which may show tumor dedifferentiation associated with increased mortality. Compared to EML4-ALK, STRN-ALK may be more common in PDTC, and ~10% of ALK fusions occur to rare gene partners. When ALK fusion is detected preoperatively in FNA samples, malignancy should be expected.