Exploring the molecular landscape of cutaneous mixed tumors characterized by TRPS1::PLAG1 gene fusion.

The histological similarities between pleomorphic adenomas (PAs) and cutaneous mixed tumors (CMTs) found in certain facial regions can create a diagnostic challenge. Molecular findings reveal common genetic profiles, particularly PLAG1 rearrangements in both PA and CMT. Although molecular distinctions have received limited attention, our observations indicate multiple cases of CMTs carrying the TRPS1::PLAG1 fusion. This clinical experience has driven our investigation into the potential diagnostic utility of TRPS1::PLAG1 fusions for determining tumor origin. Two cohorts consisting of 46 cases of CMT and 45 cases of PA of the salivary glands were obtained from French institutions and reviewed by specialists in each subspecialty. RNA sequencing analysis was conducted to identify the molecular features of cases harboring PLAG1. Clinical, pathological, and molecular data were collected. In this study, cases of CMT exhibited recurrent gene fusions, primarily TRPS1::PLAG1 (74%). These tumors shared characteristic histological features, including tubuloductal differentiation in 55% of cases and squamous metaplasia in varying proportions. In contrast, cases of PA had gene fusions involving PLAG1 with various gene partners, with only one case in which TRPS1::PLAG1 was identified. This disparity was also observed at the transcriptomic level between TRPS1::PLAG1 CMTs and other tumors. However, TRPS1 immunostaining did not correlate with TRPS1::PLAG1 fusion. In conclusion, we report that recurrent TRPS1::PLAG1 fusion CMTs exhibit similar characteristic histological features, including tubuloductal differentiation that is associated with squamous metaplasia in around half of cases. Detection of this fusion could be valuable in correctly identifying the origin of these tumors. © 2024 The Pathological Society of Great Britain and Ireland.

A novel SMARCA2-CREM fusion expending the molecular spectrum of salivary gland hyalinazing clear cell carcinoma beyond the FET genes.

Hyalinizing clear cell carcinoma (HCCC) is a rare salivary gland carcinoma with a generally indolent behavior, characterized by recurrent chromosomal translocation involving EWSR1 (22q12.2) leading to two fusion genes EWSR1::ATF1 or EWSR1::CREM. We report one case of HCCC with a novel SMARCA2::CREM fusion, identified by targeted RNA next generation sequencing by LD-RT-PCR, which has until now never been described in salivary glands. The exon 4 of SMARCA2 is fused to exon 5 of CREM. This fusion has been described previously in only one tumor, a central nervous system tumor (intracranial mesenchymal tumor) but not in other FET::CREB fused tumors. This fusion was confirmed by CREM break-apart FISH and reverse transcriptase polymerase chain reaction (RT-PCR). The tumor cells showed retained expression of INI1, SMARCA2, and SMARCA4 by immunohistochemistry. We compare its clinical, histopathological, immunophenotypic, genetic features with those previously described in HCCC, FET::CREB fusion-positive. Our results added data suggesting that different histomolecular tumor subtypes seem to be included within the terminology "HCCC, FET::CREB fusion-positive," and that further series of cases are needed to better characterize them.

[Fusion genes in salivary gland tumors]. / Les tumeurs des glandes salivaires associées à des transcrits de fusion.

Salivary gland tumors represent a diagnostic challenge for pathologists due to their rarity, their very wide histopathological and immuno-phenotypic spectrum, and the recent identification of new entities. This article presents the main molecular characteristics of these tumors in order to allow any pathologist to perceive the diagnostic tracks of these ENT tumors and to better guide the molecular approach to establish the diagnosis and guide therapy.

Detection of salivary gland and sinonasal fusions by a next-generation sequencing based, ligation-dependent, multiplex RT-PCR assay.

AIMS: The discovery of tumour type-specific gene fusion oncogenes in benign and malignant salivary gland and sinonasal (SGSN) tumours has significantly increased our knowledge about their molecular pathology and classification. METHODS AND RESULTS: We developed a new targeted multiplexed next-generation sequencing (NGS)-based method that utilizes ligation dependent reverse-transcriptase polymerase chain reaction (LD-RT-PCR) to detect oncogenic fusion transcripts involving 116 genes, leading to 96 gene fusions known to be recurrently rearranged in these tumours. In all, 180 SGSN tumours (formalin-fixed, paraffin-embedded samples, 141 specimens and 39 core needle biopsies) from the REFCORpath (French network for rare head and neck cancers) with previously identified fusion genes by fluorescent in situ hybridisation (FISH), RT-PCR, or molecular immunohistochemistry were selected to test its specificity and sensitivity and validate its diagnostic use. Tested tumours encompassed 14 major tumours types, including secretory carcinoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, salivary gland intraductal carcinoma, clear cell carcinoma, pleomorphic adenoma, adamantinoma-like Ewing Sarcoma, EWSR1::COLCA2 sinonasal sarcoma, DEK::AFF2 sinonasal carcinoma, and biphenotypic sinonasal sarcoma. In-frame fusion transcripts were detected in 97.8% of cases (176/180). Gene fusion assay results correlated with conventional techniques (immunohistochemistry [IHC], FISH, and RT-PCR) in 176/180 tumours (97.8%). CONCLUSION: This targeted multiplexed NGS-based LD-RT-PCR method is a robust, highly sensitive method for the detection of recurrent gene fusions from routine clinical SGSN tumours. It can be easily customized to cover new fusions. These results are promising for implementing an integrated NGS system to rapidly detect genetic aberrations, facilitating accurate, genomics-based diagnoses, and accelerate time to precision therapies in SGSN tumours.

Detection of sarcoma fusions by a next-generation sequencing based-ligation-dependent multiplex RT-PCR assay.

Morphological, immunohistochemical, and molecular methods often need to be combined for accurate diagnosis and optimal clinical management of sarcomas. Here, we have developed, a new molecular diagnostic assay, for the detection of gene fusions in sarcomas. This targeted multiplexed next-generation sequencing (NGS)-based method utilizes ligation dependent reverse-transcriptase polymerase chain reaction (LD-RT-PCR-NGS) to detect oncogenic fusion transcripts involving 137 genes, leading to 139 gene fusions known to be recurrently rearranged in soft-tissue and bone tumors. 158 bone and soft-tissue tumors with previously identified fusion genes by fluorescent in situ hybridization (FISH) or RT-PCR were selected to test the specificity and the sensitivity of this assay. RNA were extracted from formalin-fixed paraffin-embedded (n = 143) or frozen (n = 15) material (specimen; n = 42 or core needle biopsies; n = 116). Tested tumors encompassed 23 major translocation-related sarcomas types, including Ewing and Ewing-like sarcomas, rhabdomyosarcomas, desmoplastic small round-cell tumors, clear-cell sarcomas, infantile fibrosarcomas, endometrial stromal sarcomas, epithelioid hemangioendotheliomas, alveolar soft-part sarcomas, biphenotypic sinonasal sarcomas, extraskeletal myxoid chondrosarcomas, myxoid/round-cell liposarcomas, dermatofibrosarcomas protuberans and solitary fibrous tumors. In-frame fusion transcripts were detected in 98.1% of cases (155/158). Gene fusion assay results correlated with conventional techniques (FISH and RT-PCR) in 155/158 tumors (98.1%). These data demonstrate that this assay is a rapid, robust, highly sensitive, and multiplexed targeted RNA sequencing assay for the detection of recurrent gene fusions on RNA extracted from routine clinical specimens of sarcomas (formalin-fixed paraffin-embedded or frozen). It facilitates the precise diagnosis and identification of tumors with potential targetable fusions. In addition, this assay can be easily customized to cover new fusions.

Improving high-resolution copy number variation analysis from next generation sequencing using unique molecular identifiers.

BACKGROUND: Recently, copy number variations (CNV) impacting genes involved in oncogenic pathways have attracted an increasing attention to manage disease susceptibility. CNV is one of the most important somatic aberrations in the genome of tumor cells. Oncogene activation and tumor suppressor gene inactivation are often attributed to copy number gain/amplification or deletion, respectively, in many cancer types and stages. Recent advances in next generation sequencing protocols allow for the addition of unique molecular identifiers (UMI) to each read. Each targeted DNA fragment is labeled with a unique random nucleotide sequence added to sequencing primers. UMI are especially useful for CNV detection by making each DNA molecule in a population of reads distinct. RESULTS: Here, we present molecular Copy Number Alteration (mCNA), a new methodology allowing the detection of copy number changes using UMI. The algorithm is composed of four main steps: the construction of UMI count matrices, the use of control samples to construct a pseudo-reference, the computation of log-ratios, the segmentation and finally the statistical inference of abnormal segmented breaks. We demonstrate the success of mCNA on a dataset of patients suffering from Diffuse Large B-cell Lymphoma and we highlight that mCNA results have a strong correlation with comparative genomic hybridization. CONCLUSION: We provide mCNA, a new approach for CNV detection, freely available at https://gitlab.com/pierrejulien.viailly/mcna/ under MIT license. mCNA can significantly improve detection accuracy of CNV changes by using UMI.

An improved assay for detection of theranostic gene translocations and MET exon 14 skipping in thoracic oncology.

Theranostic translocations may be difficult to detect by routine techniques, especially when specimens are exiguous. We recently demonstrated in a series of translocated lung adenocarcinomas that LD-RT-PCR (ligation-dependent reverse transcription polymerase chain reaction) assay could identify ALK, ROS1 and RET rearrangements with 64% sensitivity and 100% specificity. Here, we report an upgraded version of this assay used in a routine prospective cohort of lung carcinomas. Newly diagnosed lung carcinomas referred to the Rouen molecular platform between 15/05/2018 and 15/05/2019 for ALK and ROS1 IHC, genotyping (SNaPshot© +/- high-throughput genotyping) and sometimes FISH (standard routine process) were tested prospectively in parallel with the LD-RT-PCR assay designed to detect at one go ALK, ROS1 and RET translocations and MET exon 14 skipping. 413 tumors from 396 patients were included. LD-RT-PCR had a global sensitivity of 91.43% (standard routine process: 80%), with a specificity of 100%. It detected 15/18 ALK and 4/4 ROS1 translocated tumors, but also 6/6 tumors with MET exon 14 skipping retrieved by genotyping. In addition, it retrieved 7 alterations missed by the routine process, then confirmed by other means: 5 MET exon 14 skipping and 2 RET translocated tumors. Finally, it allowed to deny an effect on MET exon 14 skipping for 8 mutations detected by routine genotyping. We successfully implemented LD-RT-PCR in routine analysis. This technique is cheap, fast, sensitive, specific, and easily upgradable (e.g., NTRK translocations), but still requires IHC to be performed in parallel. Owing to its advantages, we recommend considering it, in parallel with IHC and genotyping, as an excellent cost-effective alternative, for the systematic testing of lung adenocarcinoma, to FISH and to more expensive and complex assays such as RNA-seq.

Sinonasal Squamous Cell Carcinoma with DEK::AFF2 Rearrangement : An Aggressive Cancer with Bland Morphology.

AIMS: DEK::AFF2 squamous cell carcinoma is a recently described cancer entity, with 29 cases reported to date. Occasionally, these carcinomas appear deceptively indistinguishable; however, specific morphological and phenotypic features suggest the presence of this rearrangement. However, the prognostic value of this diagnosis remains unclear. We aimed to report a new case series with histological, molecular, and clinical features. METHODS: We collected data from 15 patients and investigated their phenotypes, including the expression profiles of CK7, P63/P40, PDL1, AFF2, and P16, morphological features, and associated prognostic data. We analyzed these data along with the previously published data. RESULTS: Most of these cases exhibited indicative morphological features, such as exophytic and endophytic papillary growth, nuclear monomorphism, and abundant neutrophil-rich inflammatory infiltrates. Immunohistochemical analysis revealed the expression of AFF2 and squamous cell markers in all the patients. Overexpression of P16 was not detected, whereas CK7 and PDL1 were expressed variably. In our study cohort, a 50% progression or recurrence rate, 25% lymph node metastasis, 17% distant metastasis, and 18% disease-related death were identified, with a short follow-up time. CONCLUSION: DEK::AFF2 squamous cell carcinoma incidence is probably underestimated. The low-grade appearance of these tumors sometimes limits their detection. The rates of recurrence and metastasis seem to be high despite an often bland morphology. We propose AFF2 immunohistochemistry as an effective tool, and a diagnostic algorithm has been established to support accurate diagnosis of these tumors.

Analysis of immunoglobulin/T-cell receptor repertoires by high-throughput RNA sequencing reveals a continuous dynamic of positive clonal selection in follicular lymphoma.

Follicular lymphoma (FL) course is highly variable, making its clinical management challenging. In this incurable and recurring pathology, the interval between relapses tends to decrease while aggressiveness increases, sometimes resulting in the transformation to higher-grade lymphoma. These evolutions are particularly difficult to anticipate, resulting from complex clonal evolutions where multiple subclones compete and thrive due to their capacity to proliferate and resist therapies. Here, to apprehend further these processes, we used a high-throughput RNA sequencing approach to address simultaneously the B-cell immunoglobulin repertoires and T-cell immunoglobulin repertoires repertoires of lymphoma cells and their lymphoid microenvironment in a large cohort of 131 FL1/2-3A patients. Our data confirm the existence of a high degree of intra-clonal heterogeneity in this pathology, resulting from ongoing somatic hyper-mutation and class switch recombination. Through the evaluation of the Simpson ecological-diversity index, we show that the contribution of the cancerous cells increases during the course of the disease to the detriment of the reactive compartment, a phenomenon accompanied by a concomitant decrease in the diversity of the tumoral population. Clonal evolution in FL thus contrasts with many tumors, where clonal heterogeneity steadily increases over time and participates in treatment evasion. In this pathology, the selection of lymphoma subclones with proliferative advantages progressively outweighs clonal diversification, ultimately leading in extreme cases to transformation to high-grade lymphoma resulting from the rapid emergence of homogeneous subpopulations.

Characterization of a Molecularly Distinct Subset of Oncocytic Pleomorphic Adenomas/Myoepitheliomas Harboring Recurrent ZBTB47-AS1::PLAG1 Gene Fusion.

Recurrent gene fusions are common in salivary gland tumors including benign tumors, such as pleomorphic adenoma (PA) and myoepithelioma (ME). In cases where chromosomal rearrangement is identified in the pleomorphic adenoma gene 1 (PLAG1) gene, different gene partners are found. Oncocytic metaplasia, characterized by oncocytes with abundant eosinophilic granular cytoplasm and hyperchromatic nuclei, is a well-known phenomenon in salivary gland neoplasms. However, the pure oncocytic variant of PA/ME showed PLAG1 gene rearrangements involving various gene partners at the molecular level, without any recurrent fusion being found. Our study includes 20 cases of PA/ME, with 11 females and 9 males. The age of patients ranged from 37 to 96 years, with a median age of 62.8 years. Most tumors originate from the parotid gland. The median size of the tumor was 26.5 mm (range: 13 to 60 mm). Among the 20 cases, 14 were a pure oncocytic variant of PA/ME, whereas 6 cases showed focal oncocytic or oncocytic-like aspects. Molecular studies on 20 cases of PA/ME were conducted. A novel recurrent ZBTB47-AS1::PLAG1 fusion was identified in 6 of 12 cases with pure oncocytic metaplasia, whereas the other cases had PLAG1 gene fusion with different gene partners. The transcriptomic analysis of the cases harboring ZBTB47-AS1::PLAG1 fusion demonstrated that these tumors have a distinct molecular profile from conventional PA/ME. This study reveals a unique subset in the oncocytic PA/ME spectrum characterized by pure oncocytic morphology with larger oncocytic cells and recurrent ZBTB47-AS1::PLAG1 fusion. It also highlights the transcriptomic distinctness of salivary gland adenomas with pure oncocytic metaplasia in the spectrum of salivary gland neoplasms. Further studies are needed to better understand the oncocytic variant of PA/ME and to determine the true nature of oncocytic cells in PA/ME.

Beneath HMGA2 alterations in pleomorphic adenomas: Pathological, immunohistochemical, and molecular insights.

AIMS: Most salivary gland neoplasms are distinguished by specific recurrent gene fusions. Recently, a subset of pleomorphic adenomas (PAs) originated from the parotid gland harboring the HMGA2:WIF1 fusion was described with a canalicular adenoma-like morphology and a greater propensity for recurrence and carcinomatous transformation. METHODS AND RESULTS: This study delineates the clinicopathological attributes of 54 cases of PAs exhibiting HMGA2 alterations, predominantly characterized by the HMGA2:WIF1 fusion, alongside a comparative analysis of their morphological and immunohistochemical profiles. The cohort consisted of 23 females and 31 males (n = 54), mean age was 56.7 (25-84), tumors predominantly originated from the parotid gland (94.4%, 51/54), with 3 cases from seromucous glands (5.6%). Mean tumor size was 2.6 cm (0.8-7.5). No clinical difference (demographic, follow-up) was observed among histological subsets (conventional, hybrid, and pure). Complete excision was performed in all cases, with follow-up data available for 41% (22/54) of patients, showing 13.6% of recurrence (3/22) between 5 and 8 months. Various histological growth patterns were identified, with the pure hypercellular monomorphic subset being the most prevalent. The HMGA2:WIF1 gene was identified in all subsets without any particular predominance. Novel gene partners of HMGA2 were identified, comprising NRXN1, INPP4B, MSRB3, PHLDA1, and FLJ41278. CONCLUSIONS: The present study reports that the HMGA2:WIF1 gene fusion was present in all subsets of PAs without significant predominance. However, further investigations are warranted to explore the relationship between histological subsets of PAs and the molecular alterations underlying them.

Pan-TRK Immunohistochemistry Is Highly Correlated With NTRK3 Gene Rearrangements in Salivary Gland Tumors.

AIMS: Secretory carcinoma (SC) is characterized by ETV6 rearrangements, most often ETV6-NTRK3 fusion. Given its histologic overlap with other salivary gland tumors (SGTs), SCs can be difficult to diagnose without genetic confirmation. A recently developed pan-TRK (tropomyosin receptor kinase) antibody shows promise for identifying tumors with NTRK (neurotrophic tyrosine kinase receptor 3) fusions. The aim of this study was to evaluate the utility of pan-TRK immunohistochemistry in distinguishing SCs from mimics and selecting patients eligible for TRK inhibitor clinical trials. We examined whole-tissue sections from 111 SGTs with molecular characterization, including 26 SCs (23 with ETV6-NTRK3 fusion and 3 with ETV6-RET fusion detected by ligation-dependent reverse transcription-polymerase chain reaction, next-generation sequencing and 85 non-SC SGTs (no ETV6-NTRK3 fusion). Immunohistochemistry was performed with a pan-TRK rabbit monoclonal antibody. When any pan-TRK staining (nuclear or cytoplasmic with any staining intensity) was considered to indicate positivity, 22 of 23 SCs with ETV6-NTRK3 fusion (95.7%) and 33 of 85 non-SC (38.8%) salivary neoplasms were positive, mainly basal cell adenoma, pleomorphic adenomas, adenoid cystic carcinomas, and epithelial-myoepithelial carcinomas. All SCs with ETV6-RET fusion were entirely negative. When only nuclear pan-TRK staining with any staining intensity was considered positive, 18 of 23 SCs with ETV6-NTRK3 fusion (78.3%) were positive, 11 among them with diffuse staining (>30% of cells). All non-SCs and SCs with ETV6-RET fusion were entirely negative. In comparison to molecular analysis (ligation-dependent reverse transcription-polymerase chain reaction, next-generation sequencing), nuclear pan-TRK IHC has a sensitivity of 78.3% and a specificity of 100% for diagnosing SCs with ETV6-NTRK3 fusion, 69% and 100% for SCs (all fusions). Pan-TRK is a reasonable screening test for diagnosing SCs among SGTs when taking only nuclear staining into account. Although pan-TRK expression is not entirely sensitive for SCs, nuclear staining is highly specific for SCs with ETV6-NTRK3 fusion. The lack of pan-TRK immunoreactivity in a subset of SCs is suggestive of atypical exons 4 to 14 or exons 5 to 14 ETV6-NTRK3 fusion or non-NTRK alternative fusion partners such as ETV6-RET. Pan-TRK staining can serve as a strong diagnostic marker to distinguish SC from it mimics and to select patients eligible for TRK inhibitor clinical trials.

Detection of Gene Fusion Transcripts in Peripheral T-Cell Lymphoma Using a Multiplexed Targeted Sequencing Assay.

The genetic basis of peripheral T-cell lymphoma (PTCL) is complex and encompasses several recurrent fusion transcripts discovered over the past years by means of massive parallel sequencing. However, there is currently no affordable and rapid technology for their simultaneous detection in clinical samples. Herein, we developed a multiplex ligation-dependent RT-PCR-based assay, followed by high-throughput sequencing, to detect 33 known PTCL-associated fusion transcripts. Anaplastic lymphoma kinase (ALK) fusion transcripts were detected in 15 of 16 ALK-positive anaplastic large-cell lymphomas. The latter case was further characterized by a novel SATB1_ALK fusion transcript. Among 239 other PTCLs, representative of nine entities, non-ALK fusion transcripts were detected in 24 samples, mostly of follicular helper T-cell (TFH) derivation. The most frequent non-ALK fusion transcript was ICOS_CD28 in nine TFH-PTCLs, one PTCL not otherwise specified, and one adult T-cell leukemia/lymphoma, followed by VAV1 rearrangements with multiple partners (STAP2, THAP4, MYO1F, and CD28) in five samples (three PTCL not otherwise specified and two TFH-PTCLs). The other rearrangements were CTLA4_CD28 (one TFH-PTCL), ITK_SYK (two TFH-PTCLs), ITK_FER (one TFH-PTCL), IKZF2_ERBB4 (one TFH-PTCL and one adult T-cell leukemia/lymphoma), and TP63_TBL1XR1 (one ALK-negative anaplastic large-cell lymphoma). All fusions detected by our assay were validated by conventional RT-PCR and Sanger sequencing in 30 samples with adequate material. The simplicity and robustness of this targeted multiplex assay make it an attractive tool for the characterization of these heterogeneous diseases.

Combining gene expression profiling and machine learning to diagnose B-cell non-Hodgkin lymphoma.

Non-Hodgkin B-cell lymphomas (B-NHLs) are a highly heterogeneous group of mature B-cell malignancies. Their classification thus requires skillful evaluation by expert hematopathologists, but the risk of error remains higher in these tumors than in many other areas of pathology. To facilitate diagnosis, we have thus developed a gene expression assay able to discriminate the seven most frequent B-cell NHL categories. This assay relies on the combination of ligation-dependent RT-PCR and next-generation sequencing, and addresses the expression of more than 130 genetic markers. It was designed to retrieve the main gene expression signatures of B-NHL cells and their microenvironment. The classification is handled by a random forest algorithm which we trained and validated on a large cohort of more than 400 annotated cases of different histology. Its clinical relevance was verified through its capacity to prevent important misclassification in low grade lymphomas and to retrieve clinically important characteristics in high grade lymphomas including the cell-of-origin signatures and the MYC and BCL2 expression levels. This accurate pan-B-NHL predictor, which allows a systematic evaluation of numerous diagnostic and prognostic markers, could thus be proposed as a complement to conventional histology to guide the management of patients and facilitate their stratification into clinical trials.