Melanomas with activating RAF1 fusions: clinical, histopathologic, and molecular profiles

Targeting RAF1 gene fusions with MEK inhibition in metastatic melanoma

The biological and clinical relevance of gene fusions in melanoma is unknown. Reports and preclinical data have suggested that tumor cells with specific rearrangements such as RAF1 gene fusions could be therapeutically targeted. To investigate the relevance of targeted therapy in patients with melanoma harboring RAF1 gene fusions, we reviewed records of 1268 melanoma patients with targeted sequencing data at the Dana-Farber Cancer Institute. We identified 9 cases and report here on their clinicopathologic characteristics. We describe the favorable outcome of 2 patients who received MEK inhibitor therapy, including 1 patient with a durable response. We coalesced our data with published reports of patients with RAF1 gene fusions who were treated with targeted therapy. We find that single-agent MEK inhibition has anti-tumor activity in melanoma patients harboring an RAF1 gene fusion, and we propose that patients with RAF1 gene fusions should be considered for single-agent MEK inhibitor therapy.

Somatic structural variants drive distinct modes of oncogenesis in melanoma

The diversity of structural variants (SVs) in melanoma and how they impact oncogenesis are incompletely known. We performed harmonized analysis of SVs across melanoma histologic and genomic subtypes, and we identified distinct global properties between subtypes. These included the frequency and size of SVs and SV classes, their relation to chromothripsis events, and the impact on cancer-related genes of SVs that alter topologically associated domain (TAD) boundaries. Following our prior identification of double-stranded break repair deficiency in a subset of triple-wild-type cutaneous melanoma, we identified MRE11 and NBN loss-of-function SVs in melanomas with this mutational signature. Experimental knockouts of MRE11 and NBN, followed by olaparib cell viability assays in melanoma cells, indicated that dysregulation of each of these genes may cause sensitivity to PARP inhibitors in cutaneous melanomas. Broadly, harmonized analysis of melanoma SVs revealed distinct global genomic properties and molecular drivers, which may have biological and therapeutic impact.

Kinase Fusions in Spitz Melanocytic Tumors: The Past, the Present, and the Future

In recent years, particular interest has developed in molecular biology applied to the field of dermatopathology, with a focus on nevi of the Spitz spectrum. From 2014 onwards, an increasing number of papers have been published to classify, stratify, and correctly frame molecular alterations, including kinase fusions. In this paper, we try to synthesize the knowledge gained in this area so far. In December 2023, we searched Medline and Scopus for case reports and case series, narrative and systematic reviews, meta-analyses, observational studies-either longitudinal or historical, case series, and case reports published in English in the last 15 years using the keywords spitzoid neoplasms, kinase fusions, ALK, ROS1, NTRK (1-2-3), MET, RET, MAP3K8, and RAF1. ALK-rearranged Spitz tumors and ROS-1-rearranged tumors are among the most studied and characterized entities in the literature, in an attempt (although not always successful) to correlate histopathological features with the probable molecular driver alteration. NTRK-, RET-, and MET-rearranged Spitz tumors present another studied and characterized entity, with several rearrangements described but as of yet incomplete information about their prognostic significance. Furthermore, although rarer, rearrangements of serine-threonine kinases such as BRAF, RAF1, and MAP3K8 have also been described, but more cases with more detailed information about possible histopathological alterations, mechanisms of etiopathogenesis, and also prognosis are needed. The knowledge of molecular drivers is of great interest in the field of melanocytic diagnostics, and it is important to consider that in addition to immunohistochemistry, molecular techniques such as FISH, PCR, and/or NGS are essential to confirm and classify the different patterns of mutation. Future studies with large case series and molecular sequencing techniques are needed to allow for a more complete and comprehensive understanding of the role of fusion kinases in the spitzoid tumor family.

The role of CRAF in cancer progression: from molecular mechanisms to precision therapies

The RAF family of kinases includes key activators of the pro-tumourigenic mitogen-activated protein kinase pathway. Hyperactivation of RAF proteins, particularly BRAF and CRAF, drives tumour progression and drug resistance in many types of cancer. Although BRAF is the most studied RAF protein, partially owing to its high mutation incidence in melanoma, the role of CRAF in tumourigenesis and drug resistance is becoming increasingly clinically relevant. Here, we summarize the main known regulatory mechanisms and gene alterations that contribute to CRAF activity, highlighting the different oncogenic roles of CRAF, and categorize RAF1 (CRAF) mutations according to the effect on kinase activity. Additionally, we emphasize the effect that CRAF alterations may have on drug resistance and how precision therapies could effectively target CRAF-dependent tumours. Here, we discuss preclinical and clinical findings that may lead to improved treatments for all types of oncogenic RAF1 alterations in cancer.

RAF1-rearranged Spindle Cell Mesenchymal Tumor With Calcification and Heterotopic Ossification: A Case Report and Review of Literature

We report an exceptional case of a spindle cell mesenchymal tumor with S100 and CD34 co-reactivity, which harbored a SLMAP::RAF1 fusion. To the best of our knowledge, this is the second case of a spindle cell mesenchymal tumor with S100 and CD34 co-reactivity with this specific fusion. Remarkable is the presence of calcification and heterotopic ossification in the center of our lesion, a feature that, to our knowledge, has not been described yet in RAF1-rearranged spindle cell mesenchymal tumors.

Novel ATG7::RAF1 gene fusion in malignant glomus tumor

Glomus tumors are classified as members of the perivascular myoid family of tumors. Nearly half of these show NOTCH-gene fusions and a smaller subset has BRAF V600E mutations. Here, we report a novel ATG7::RAF1 fusion in malignant glomus tumor occurring in a 40-year-old female which has not been reported in the malignant glomus tumor before. A 40-year-old female presented with a persistent lateral heel pain and an increase in the size of a mass along the lateral ankle for nearly 10 years. Resected specimen showed a well circumscribed lesion composed of spindled and epithelioid cells with moderate nuclear atypia and mitotic figures (7/10 high-power fields) including atypical forms without any necrosis, lymphovascular, or perineural invasion. The tumor was positive for smooth muscle actin, smooth muscle myosin heavy chain, H-caldesmon, collagen type IV, and discovered on gastronintestinal stromal tumors-1 but negative for AE1/3, desmin, S-100, CD34, and CD117. RNA sequencing showed presence of ATG7-RAF1 fusion. This fusion has not been reported in the malignant glomus tumor before. Future studies on larger cohorts are needed to ascertain the biological significance of these tumors with novel gene fusions.

Targeting CRAF kinase in anti-cancer therapy: progress and opportunities

The RAS/mitogen-activated protein kinase (MAPK) signaling cascade is commonly dysregulated in human malignancies by processes driven by RAS or RAF oncogenes. Among the members of the RAF kinase family, CRAF plays an important role in the RAS-MAPK signaling pathway, as well as in the progression of cancer. Recent research has provided evidence implicating the role of CRAF in the physiological regulation and the resistance to BRAF inhibitors through MAPK-dependent and MAPK-independent mechanisms. Nevertheless, the effectiveness of solely targeting CRAF kinase activity remains controversial. Moreover, the kinase-independent function of CRAF may be essential for lung cancers with KRAS mutations. It is imperative to develop strategies to enhance efficacy and minimize toxicity in tumors driven by RAS or RAF oncogenes. The review investigates CRAF alterations observed in cancers and unravels the distinct roles of CRAF in cancers propelled by diverse oncogenes. This review also seeks to summarize CRAF-interacting proteins and delineate CRAF's regulation across various cancer hallmarks. Additionally, we discuss recent advances in pan-RAF inhibitors and their combination with other therapeutic approaches to improve treatment outcomes and minimize adverse effects in patients with RAF/RAS-mutant tumors. By providing a comprehensive understanding of the multifaceted role of CRAF in cancers and highlighting the latest developments in RAF inhibitor therapies, we endeavor to identify synergistic targets and elucidate resistance pathways, setting the stage for more robust and safer combination strategies for cancer treatment.

Prevalence of RAF1 Aberrations in Metastatic Cancer Patients: Real-World Data

PURPOSE

Therapeutic targeting of RAF1 is a promising cancer treatment, but the relationship between clinical features and RAF1 aberrations in terms of the MAPK signaling pathway is poorly understood in various solid tumors.

METHODS

Between October 2019 and June 2023 at Samsung Medical Center, 3895 patients with metastatic solid cancers underwent next-generation sequencing (NGS) using TruSight Oncology 500 (TSO500) assays as routine clinical practice. We surveyed the incidence of RAF1 aberrations including mutations (single-nucleotide variants [SNVs]), amplifications (copy number variation), and fusions.

RESULTS

Among the 3895 metastatic cancer patients, 77 (2.0%) exhibited RAF1 aberrations. Of these 77 patients, 44 (1.1%) had RAF1 mutations (SNV), 25 (0.6%) had RAF1 amplifications, and 10 (0.3%) had RAF1 fusions. Among the 10 patients with RAF1 fusions, concurrent RAF1 amplifications and RAF1 mutations were detected in one patient each. The most common tumor types were bladder cancer (11.5%), followed by ampulla of Vater (AoV) cancer (5.3%), melanoma (3.0%), gallbladder (GB) cancer (2.6%), and gastric (2.3%) cancer. Microsatellite instability high (MSI-H) tumors were observed in five of 76 patients (6.6%) with RAF1 aberrations, while MSI-H tumors were found in only 2.1% of patients with wild-type RAF1 cancers (p < 0.0001).

CONCLUSION

We demonstrated that approximately 2.0% of patients with metastatic solid cancers have RAF1 aberrations according to NGS of tumor specimens.

Spitz tumor with RAF1 fusion: A report of 3 cases

Spitz tumors are melanocytic neoplasms morphologically characterized by spindled and/or epithelioid cells and specific stromal and epidermal changes associated with mutually exclusive fusion kinases involving ALK, ROS1, NTRK1, NTRK2, NTRK3, MET and RET, BRAF and MAP3K8 genes or, less commonly, HRAS mutation. RAF1 fusions have been recently detected in cutaneous melanocytic neoplasms, including conventional melanoma, congenital nevus and BAP-1 inactivated tumors. We report herewith three Spitz neoplasms with a RAF1 fusion, including a previously reported CTDSPL::RAF1 fusion and two novel PPAP2B::RAF1 and ATP2B4::RAF1 fusions. Two cases were classified as Spitz nevus, while the remaining neoplasm was classified as Spitz melanoma at the time of the diagnosis, given 9p21 homozygous deletion and positive sentinel lymph node biopsy. We suggest that RAF1 fused melanocytic neoplasms can represent a novel subgroup of Spitz tumors, with a RAF1 fusion representing an oncogenic driver.

Recurrent TRAK1::RAF1 Fusions in pediatric low-grade gliomas

Fusions involving CRAF (RAF1) are infrequent oncogenic drivers in pediatric low-grade gliomas, rarely identified in tumors bearing features of pilocytic astrocytoma, and involving a limited number of known fusion partners. We describe recurrent TRAK1::RAF1 fusions, previously unreported in brain tumors, in three pediatric patients with low-grade glial-glioneuronal tumors. We present the associated clinical, histopathologic and molecular features. Patients were all female, aged 8 years, 15 months, and 10 months at diagnosis. All tumors were located in the cerebral hemispheres and predominantly cortical, with leptomeningeal involvement in 2/3 patients. Similar to previously described activating RAF1 fusions, the breakpoints in RAF1 all occurred 5' of the kinase domain, while the breakpoints in the 3' partner preserved the N-terminal kinesin-interacting domain and coiled-coil motifs of TRAK1. Two of the three cases demonstrated methylation profiles (v12.5) compatible with desmoplastic infantile ganglioglioma (DIG)/desmoplastic infantile astrocytoma (DIA) and have remained clinically stable and without disease progression/recurrence after resection. The remaining tumor was non-classifiable; with focal recurrence 14 months after initial resection; the patient remains symptom free and without further recurrence/progression (5 months post re-resection and 19 months from initial diagnosis). Our report expands the landscape of oncogenic RAF1 fusions in pediatric gliomas, which will help to further refine tumor classification and guide management of patients with these alterations.

Entrectinib for NTRK Fusion-Positive Metastatic Melanoma Progressing on Combined PD-1 and CTLA-4 Inhibition: A Case Report

Introduction

The burden of melanoma is increasing globally. Despite the use of immunotherapy and targeted therapy, the prognosis of metastatic melanoma remains relatively poor. The integration of comprehensive molecular profiling can lead to the detection of actionable biomarkers and the expansion of treatment options, thereby prolonging cancer patient survival.

Case Presentation

We herein present the case of a female 54-year-old patient diagnosed with melanoma of the right knee, for which she underwent surgery. Patient showed progression of disease after 10 cycles of adjuvant nivolumab. Ipilimumab (1 mg/kg every 3 weeks) was added to the treatment regimen but no clinical improvement was observed. Molecular profiling was conducted based on patient tissue, and an ANXA2-NTRK3 fusion was detected in the tumor. This specific fusion has not been previously reported; however, it is in-frame and similar to other known oncogenic NTRK fusions. At the time of entrectinib initiation, the patient had clear disease progression on the right leg on standard of care immunotherapy. She was commenced on entrectinib 200 mg once daily for 2 weeks. Dose escalation was attempted, and treatment intensity was managed based on drug tolerability. Good treatment response was observed on laboratory and radiologic parameters. As of September 2023, i.e., 2.5 years after treatment initiation, patient disease continues to be controlled with entrectinib.

Conclusion

Profiling of advanced tumors is important to determine the presence of agnostic markers that can be targeted and ultimately improve the prognostic outcome of patients after the failure of standard of care.

Genomic and Transcriptional Profiling of Chinese Melanoma Patients Enhanced Potentially Druggable Targets: A Multicenter Study

BACKGROUND

In contrast to Caucasian melanoma, which has been extensively studied, there are few studies on melanoma in Asian populations. Sporadic studies reported that only 40% of Asian melanoma patients could be druggable, which was much lower than that in Caucasians. More studies are required to refine this conclusion.

METHODS

Chinese melanoma patients (n = 469) were sequentially sequenced by DNA-NGS and RNA-NGS. The genomic alterations were determined, and potentially actionable targets were investigated.

RESULTS

Patients with potential druggable targets were identified in 75% of Chinese melanoma patients by DNA-NGS based on OncoKB, which was much higher than in a previous Asian study. NRG1 fusions were first identified in melanoma. In addition, up to 11.7% (7/60) of patients in the undruggable group could be recognized as actionable by including RNA-NGS analysis. By comparing the fusion detection rate between DNA-NGS and RNA-NGS, all available samples after DNA-NGS detection were further verified by RNA-NGS. The use of RNA-NGS enhanced the proportion of druggable fusions from 2.56% to 17.27%. In total, the use of RNA-NGS increased the druggable proportion from 75% to 78%.

CONCLUSIONS

In this study, we systemically analyzed the actionable landscape of melanoma in the largest Asian cohort. In addition, we first demonstrated how DNA and RNA sequential sequencing is essential in bringing clinical benefits to more patients with melanoma.

ARID2 suppression promotes tumor progression and upregulates cytokeratin 8, 18 and β-4 integrin expression in TP53-mutated tobacco-related oral cancer and has prognostic implications

Mutations in ARID2 and TP53 genes are found to be implicated in the tobacco related tumorigeneses. However, the effect of loss of ARID2 in the TP53 mutated background in tobacco related cancer including oral cancer has not been investigated yet. Hence, in this study we knockdown ARID2 using shRNA mediated knockdown strategy in TP53 mutated oral squamous cell carcinoma (OSCC) cell line and studied its tumorigenic role. Our study revealed that suppression of ARID2 in TP53 mutated oral cancer cells increases cell motility and invasion, induces drastic morphological changes and leads to a marked increase in the expression levels of cytokeratins, and integrins, CK8, CK18 and β4-Integrin, markers of cell migration/invasion in oral cancer. ARID2 suppression also showed early onset and increased tumorigenicity in-vivo. Interestingly, transcriptome profiling revealed differentially expressed genes associated with migration and invasion in oral cancer cells including AKR1C2, NCAM2, NOS1, ADAM23 and genes of S100A family in ARID2 knockdown TP53 mutated oral cancer cells. Pathway analysis of differentially regulated genes identified "cancer pathways" and "PI3K/AKT Pathway" to be significantly dysregulated upon suppression of ARID2 in TP53 mutated OSCC cells. Notably, decreased ARID2 expression and increased CK8, CK18 expression leads to poor prognosis in Head and Neck cancer (HNSC) patients as revealed by Pan-Cancer TCGA data analysis. To conclude, our study is the first to demonstrate tumor suppressor role of ARID2 in TP53 mutated background indicating their cooperative role in OSCC, and also highlights its prognostic implications suggesting ARID2 as an important therapeutic target in OSCC.

Identification of fusions with potential clinical significance in melanoma

Though uncommon in melanoma, gene fusions may have therapeutic implications. Next generation sequencing-based clinical assays, designed to detect relevant gene fusions, mutations, and copy number changes, were performed on 750 melanomas (375 primary and 375 metastases) at our institution from 2014-2021. These included 599 (80%) cutaneous, 38 (5%) acral, 11 (1.5%) anorectal, 23 (3%) sinonasal, 27 (3.6%) eye (uveal/ conjunctiva), 11 (1.5%) genital (vulva/penile), and 41 (5.5%) melanomas of unknown primary. Sixteen fusions (2%) were detected in samples from 16 patients: 12/599 (2%) cutaneous, 2/38 (5%) acral, 1/9 (11%) vulva, 1/23(4.3%) sinonasal; and 12/16 (75%) fusions were potentially targetable. We identified two novel rearrangements: NAGS::MAST2 and NOTCH1::GNB1; and two fusions that have been reported in other malignancies but not in melanoma: CANT1::ETV4 (prostate cancer) and CCDC6::RET (thyroid cancer). Additional fusions, previously reported in melanoma, included: EML4::ALK, MLPH::ALK, AGAP3::BRAF, AGK::BRAF, CDH3::BRAF, CCT8::BRAF, DIP2B::BRAF, EFNB1::RAF1, LRCH3::RAF1, MAP4::RAF1, RUFY1::RAF1, and ADCY2::TERT. Fusion positive melanomas harbored recurrent alterations in TERT and CDKN2A, among others. Gene fusions were exceedingly rare (0.2%) in BRAF/RAS/NF1-mutant tumors and were detected in 5.6% of triple wild-type melanomas. Interestingly, gene rearrangements were significantly enriched within the subset of triple wild-type melanomas that harbor TERT promoter mutations (18% versus 2%, p < 0.0001). Thirteen (81%) patients were treated with immunotherapy for metastatic disease or in the adjuvant setting. Six of 12 (50%) patients with potentially actionable fusions progressed on immunotherapy, and 3/6 (50%) were treated with targeted agents (ALK and MEK inhibitors), 2 off-label and 1 as part of a clinical trial. One patient with an AGAP3::BRAF fusion positive melanoma experienced a 30-month long response to trametinib. We show that, detecting fusions, especially in triple wild-type melanomas with TERT promoter mutations, may have a clinically significant impact in patients with advanced disease who have failed front-line immunotherapy.

Unearthing novel fusions as therapeutic targets in solid tumors using targeted RNA sequencing

Detection of oncogenic fusion genes in cancers, particularly in the diagnosis of uncertain tumors, is crucial for determining effective therapeutic strategies. Although novel fusion genes have been discovered through sequencing, verifying their oncogenic potential remain difficult. Therefore, we evaluated the utility of targeted RNA sequencing in 165 tumor samples by identifying known and unknown fusions. Additionally, by applying additional criteria, we discovered eight novel fusion genes that are expected to process oncogenicity. Among the novel fusion genes, RAF1 fusion genes were detected in two cases. PTPRG-RAF1 fusion led to an increase in cell growth; while dabrafenib, a BRAF inhibitor, reduced the growth of cells expressing RAF1. This study demonstrated the utility of RNA panel sequencing as a theragnostic tool and established criteria for identifying oncogenic fusion genes during post-sequencing analysis.

Modeling Spitz melanoma in zebrafish using sequential mutagenesis

Spitz neoplasms are a diverse group of molecularly and histologically defined melanocytic tumors with varying biologic potentials. The precise classification of Spitz neoplasms can be challenging. Recent studies have revealed recurrent fusions involving multiple kinases in a large proportion of Spitz tumors. In this study, we generated a transgenic zebrafish model of Spitz melanoma using a previously identified ZCCHC8-ROS1 fusion gene. Animals developed grossly apparent melanocytic proliferations as early as 3 weeks of age and overt melanoma as early as 5 weeks. By 7 weeks, ZCCHC8-ROS1 induced a histologic spectrum of neoplasms ranging from hyperpigmented patches to melanoma. Given the swift onset of these tumors during development, we extended this approach into adult fish using a recently described electroporation technique. Tissue-specific expression of ZCCHC8-ROS1 in adults led to melanocyte expansion without overt progression to melanoma. Subsequent electroporation with tissue-specific CRISPR, targeting only tp53 was sufficient to induce transformation to melanoma. Our model exhibits the use of sequential mutagenesis in the adult zebrafish, and demonstrates that ZCCHC8-ROS1 induces a spectrum of melanocytic lesions that closely mimics human Spitz neoplasms.

Summary: We describe the first animal model of Spitz neoplasms and demonstrate its use for modeling sequential mutagenesis and its potential for studying melanocyte development in vivo.

RAF1 promotes lymphatic metastasis of hypopharyngeal carcinoma via regulating LAGE1: an experimental research

BACKGROUND

Lymphatic metastasis was an independent prognostic risk factor for hypopharyngeal carcinoma and was the main cause of treatment failure. The purpose of this study was to screen the differential genes and investigate the mechanism of lymphatic metastasis in hypopharyngeal carcinoma.

METHODS

Transcriptome sequencing was performed on primary tumors of patients, and differential genes were screened by bioinformatics analysis. The expression of differential genes was verified by qRT-PCR, western-blotting and immunohistochemical, and prognostic value was analyzed by Kaplan-Meier and log-rank test and Cox's test. Next, FADU and SCC15 cell lines were used to demonstrate the function of differential genes both in vitro by EdU, Flow cytometry, Wound Healing and Transwell assays and in vivo by a foot-pad xenograft mice model. Proteomic sequencing was performed to screen relevant targets. In addition, in vitro and in vivo experiments were conducted to verify the mechanism of lymphatic metastasis.

RESULTS

Results of transcriptome sequencing showed that RAF1 was a significantly differential gene in lymphatic metastasis and was an independent prognostic risk factor. In vitro experiments suggested that decreased expression of RAF1 could inhibit proliferation, migration and invasion of tumor cells and promote apoptosis. In vivo experiments indicated that RAF1 could promote tumor growth and lymphatic metastasis. Proteomic sequencing and subsequent experiments suggested that LAGE1 could promote development of tumor and lymphatic metastasis, and was regulated by RAF1.

CONCLUSIONS

It suggests that RAF1 can promote lymphatic metastasis of hypopharyngeal carcinoma by regulating LAGE1, and provide a basis for the exploring of novel therapeutic target and ultimately provide new guidance for the establishment of intelligent diagnosis and precise treatment of hypopharyngeal carcinoma.

Transcriptional Profiling of Malignant Melanoma Reveals Novel and Potentially Targetable Gene Fusions

Simple Summary

Malignant melanoma is a complex disease that is estimated to claim over 7000 lives in the United States in 2021. Although recent advances in genomic technology have helped with the identification of driver variants, molecular studies and clinical trials have often focused on prevalent alterations, such as the BRAF-V600E mutation. With the inclusion of whole transcriptome sequencing, molecular profiling of melanomas has identified gene fusions and revealed gene expression profiles that are consistent with the activation of signaling pathways by common driver mutations. Patients harboring such fusions may benefit from currently approved targeted therapies and should be considered in the design of future clinical trials to further personalize treatments for patients with malignant melanoma.

Abstract

Invasive melanoma is the deadliest type of skin cancer, with 101,110 expected cases to be diagnosed in 2021. Recurrent BRAF and NRAS mutations are well documented in melanoma. Biologic implications of gene fusions and the efficacy of therapeutically targeting them remains unknown. Retrospective review of patient samples that underwent next-generation sequencing of the exons of 592 cancer-relevant genes and whole transcriptome sequencing for the detection of gene fusion events and gene expression profiling. Expression of PDL1 and ERK1/2 was assessed by immunohistochemistry (IHC). There were 33 (2.6%) cases with oncogenic fusions (14 novel), involving BRAF, RAF1, PRKCA, TERT, AXL, and FGFR3. MAPK pathway-associated genes were over-expressed in BRAF and RAF1 fusion-positive tumors in absence of other driver alterations. Increased expression in tumors with PRKCA and TERT fusions was concurrent with MAPK pathway alterations. For a subset of samples with available tissue, increased phosphorylation of ERK1/2 was observed in BRAF, RAF1, and PRKCA fusion-positive tumors. Oncogenic gene fusions are associated with transcriptional activation of the MAPK pathway, suggesting they could be therapeutic targets with available inhibitors. Additional analyses to fully characterize the oncogenic effects of these fusions may support biomarker driven clinical trials.

Novel MAP4::RAF1 Fusion in a Primary Bone Sarcoma: Expanding the spectrum of RAF1 Fusion Sarcoma

Soft tissue tumors with RAF1 fusion had been emerging as a group of tumors with peculiar histology and immunoprofile. While a case series and rare case reports of RAF1 translocated sarcoma had been reported, to our knowledge a primary bone tumor with RAF1 translocation and fusion partner with MAP4 had not been described in the literature. The patient was a 60-year-old lady, with strong family history of breast cancer, who presented with pathological fracture of right humerus. X-ray revealed a 9.7 cm juxta-articular lesion of the proximal humerus, which was expansile and lytic with a non-sclerotic well defined border distally, radiologically suggestive of a giant cell tumor of bone. Excision was performed after initial biopsy. Histology showed a monomorphic low grade spindle cell lesion with prominent hyalinized stroma. Immunohistochemistry demonstrated diffuse CD34 staining, with focal staining for S100. Gene sequencing for histone 3 H3 genes was negative for hotspot mutation. Targeted RNA-seq sequencing revealed the presence of MAP4::RAF1 fusion, which was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and fluorescence in-situ hybridization (FISH) break-apart probes involving both genes. The overall features were consistent with a primary bone sarcoma with RAF1 fusion. This report expanded the spectrum of RAF1 fusion sarcoma and was the first report documenting its primary occurrence in bone.

Pan-tumor screening for NTRK gene fusions using pan-TRK immunohistochemistry and RNA NGS fusion panel testing

Targetable NTRK gene fusions can be detected across tumor types using methodologies such as pan-TRK IHC, DNA or RNA NGS testing, or FISH. Challenges for implementation of clinical testing for NTRK fusions may arise due to the range in NTRK fusion prevalence across tumors, endogenous levels of TRK expression in tissues, and the large number of potential fusion partners. In this study, we examined our experience evaluating driver mutation negative lung, urothelial or cholangiocarcinoma cases, in addition to cases with positive, equivocal, or weak staining by pan-TRK IHC for NTRK fusions. 63/127 (49.6%) of these cases were positive for pan-TRK IHC, of which 71.4% showed weak or focal staining, potentially due to physiologic or non-specific TRK expression. Of these 127 cases, 4 harbored a NTRK fusion (1 fusion was seen in two separate samples from the same patient) as confirmed by RNA fusion panel testing. Pan-TRK IHC was positive in 1 case with TPM3-NTRK1 fusion, equivocal in 1 case with GOLGA4-NTRK3 fusion, and negative in 2 samples with ADAM19-NTRK3 fusion. Our findings show that we were able to successfully identify NTRK fusions that resulted in targeted therapy. However, our results suggest limited sensitivity of pan-TRK IHC for NTRK3 fusions, and that the reduced specificity for pan-TRK IHC in tumors with physiologic or non-specific TRK expression, results in false positive samples that require confirmatory testing by RNA based NGS.

Using deep learning to identify bladder cancers with FGFR-activating mutations from histology images

BACKGROUND

In recent years, the fibroblast growth factor receptor (FGFR) pathway has been proven to be an important therapeutic target in bladder cancer. FGFR-targeted therapies are effective for patients with FGFR mutation, which can be discovered through genetic sequencing. However, genetic sequencing is not commonly performed at diagnosis, whereas a histologic assessment of the tumor is. We aim to computationally extract imaging biomarkers from existing tumor diagnostic slides in order to predict FGFR alterations in bladder cancer.

METHODS

This study analyzed genomic profiles and H&E-stained tumor diagnostic slides of bladder cancer cases from The Cancer Genome Atlas (n = 418 cases). A convolutional neural network (CNN) identified tumor-infiltrating lymphocytes (TIL). The percentage of the tissue containing TIL ("TIL percentage") was then used to predict FGFR activation status with a logistic regression model.

RESULTS

This predictive model could proficiently identify patients with any type of FGFR gene aberration using the CNN-based TIL percentage (sensitivity = 0.89, specificity = 0.42, AUROC = 0.76). A similar model which focused on predicting patients with only FGFR2/FGFR3 mutation was also found to be highly sensitive, but also specific (sensitivity = 0.82, specificity = 0.85, AUROC = 0.86).

CONCLUSION

TIL percentage is a computationally derived image biomarker from routine tumor histology that can predict whether a tumor has FGFR mutations. CNNs and other digital pathology methods may complement genome sequencing and provide earlier screening options for candidates of targeted therapies.

Novel LRRFIP2-RAF1 fusion identified in an acral melanoma: A review of the literature on melanocytic proliferations with RAF1 fusions and the potential therapeutic implications

A small subset of cutaneous melanomas harbor oncogenic gene fusions, which could potentially serve as therapeutic targets for patients with advanced disease as novel therapies are developed. Fusions involving RAF1 are exceedingly rare in melanocytic neoplasms, occurring in less than 1% of melanomas, and usually arise in tumors that are wild type for BRAF, NRAS, and NF1. We describe herein a case of acral melanoma with two satellite metastases and sentinel lymph node involvement. The melanoma had a concomitant KIT variant and LRRFIP2-RAF1 fusion. This constellation of molecular findings has not been reported previously in melanoma. We review the existing literature on melanocytic neoplasms with RAF1 fusions and discuss the potential clinical implications of this genetic event.

Melanoma with in-frame deletion of MAP2K1: a distinct molecular subtype of cutaneous melanoma mutually exclusive from BRAF, NRAS, and NF1 mutations

While the genomics of BRAF, NRAS, and other key genes influencing MAP kinase (MAPK) activity have been thoroughly characterized in melanoma, mutations in MAP2K1 (MEK1) have received significantly less attention and have consisted almost entirely of missense mutations considered secondary oncogenic drivers of melanoma. Here, we investigated melanomas with in-frame deletions of MAP2K1, alterations characterized as MAPK-activating in recent experimental models. Our case archive of clinical melanoma samples with comprehensive genomic profiling by a hybrid capture-based DNA sequencing platform was searched for MAP2K1 genetic alterations. Clinical data, pathology reports, and histopathology were reviewed for each case. From a cohort of 7119 advanced melanomas, 37 unique cases (0.5%) featured small in-frame deletions in MAP2K1. These included E102_I103del (n = 11 cases), P105_A106del (n = 8), Q58_E62del (n = 6), I103_K104del (n = 5), I99_K104del (n = 3), L98_I103del (n = 3), and E41_F53del (n = 1). All 37 were wild type for BRAF, NRAS, and NF1 genomic alterations ("triple wild-type"), representing 2.0% of triple wild-type melanomas overall (37/1882). Median age was 66 years and 49% were male. The majority arose from primary cutaneous sites (35/37; 95%) and demonstrated a UV signature when available (21/25; 84%). Tumor mutational burden was typical for cutaneous melanoma (median = 9.6 mut/Mb, range 0-35.7), and frequently mutated genes included TERTp (63%), CDKN2A (46%), TP53 (11%), PTEN (8%), APC (8%), and CTNNB1 (5%). Histopathology revealed a spectrum of appearances typical of melanoma. For comparison, we evaluated 221 cases with pathogenic missense single nucleotide variants in MAP2K1. The vast majority of melanomas with missense SNVs in MAP2K1 showed co-mutations in BRAF (58%), NF1 (23%), or NRAS (18%). In-frame deletions in MAP2K1, previously shown in experimental models to be strongly MAPK-activating, characterized a significant subset of triple wild-type melanoma (2.0%), suggesting a primary oncogenic role for these mutations. Comprehensive genomic profiling of melanomas enables detection of this alteration, which may have implications for potential therapeutic options.

Structure and Emerging Functions of LRCH Proteins in Leukocyte Biology

Actin-dependent leukocyte trafficking and activation are critical for immune surveillance under steady state conditions and during disease states. Proper immune surveillance is of utmost importance in mammalian homeostasis and it ensures the defense against pathogen intruders, but it also guarantees tissue integrity through the continuous removal of dying cells or the elimination of tumor cells. On the cellular level, these processes depend on the precise reorganization of the actin cytoskeleton orchestrating, e.g., cell polarization, migration, and vesicular dynamics in leukocytes. The fine-tuning of the actin cytoskeleton is achieved by a multiplicity of actin-binding proteins inducing, e.g., the organization of the actin cytoskeleton or linking the cytoskeleton to membranes and their receptors. More than a decade ago, the family of leucine-rich repeat (LRR) and calponin homology (CH) domain-containing (LRCH) proteins has been identified as cytoskeletal regulators. The LRR domains are important for protein-protein interactions and the CH domains mediate actin binding. LRR and CH domains are frequently found in many proteins, but strikingly the simultaneous expression of both domains in one protein only occurs in the LRCH protein family. To date, one LRCH protein has been described in drosophila and four LRCH proteins have been identified in the murine and the human system. The function of LRCH proteins is still under investigation. Recently, LRCH proteins have emerged as novel players in leukocyte function. In this review, we summarize our current understanding of LRCH proteins with a special emphasis on their function in leukocyte biology.

RAF1 Gene Fusions as a Possible Driver Mechanism in Rare BAP1-Inactivated Melanocytic Tumors: A Report of 2 Cases

BRCA1-associated protein (BAP1)-inactivated melanocytic tumor (BIMT) is a group of epithelioid melanocytic neoplasms characterized by the loss of function of BAP1, a tumor suppressor gene located on chromosome 3p21. They occur sporadically or in the setting of an autosomal-dominant cancer susceptibility syndrome that predisposes to the development of different internal malignancies. Most of these cutaneous lesions are associated with a BRAF-mutated melanocytic nevus and therefore are included in the group of combined nevi in the last WHO classification of skin tumors. Apart from a BRAF mutation, an NRAS mutation has been reported in rare cases, whereas in some lesions no driver mutation has been detected. Here, we report 2 cases of BIMTs with a BAP1 mutation and a RAF1 fusion. Both lesions proved to be BRAF and NRAS wild type and were associated with a conventional melanocytic nevus with dysplastic junctional features. We suggest that RAF1 fusions can represent an underlying driver genetic event in these cases. Our study extends the morphological and molecular spectrum in BIMTs.