Fusion Partner Genes Research Articles

The Heterogeneous Fusion Gene Landscape in Pediatric Acute Lymphoblastic Leukemia

Background: Next generation sequencing allows for the detection of expressed fusion transcripts across the transcriptome and has spurred the discovery of many novel chimeric transcripts in various cancers. Structural chromosomal rearrangements that lead to fusion transcripts are a hallmark of acute lymphoblastic leukemia (ALL) and serve as markers for diagnosis and stratification of pediatric ALL patients into prognostically relevant subgroups. Improved delineation of structural alterations in ALL could provide additional information for prognosis in ALL and for improved stratification of patients into treatment groups.Methods: To identify novel fusion transcripts in primary pediatric ALL cells we performed whole transcriptome sequencing of 134 BCP and T-ALL patient samples collected at diagnosis. Our study include samples from patients with the well-known ALL subtypes t(12;21)ETV6-RUNX1, high hyperdiploid (51-67 chromosomes), t(9;22)BCR-ABL1, 11q23/MLL and dic(9;20), in addition to patients with undefined karyotype or non-recurrent cytogenetic aberrations ("undefined" and "other") (n=58). FusionCatcher was used for the detection of somatic fusion genes, followed by a stringent filtering pipeline including gene fusion validation by Sanger sequencing in order to reduce the number of false positives. Principal component analysis (PCA) of patients with fusion genes was performed using genome wide gene expression levels and DNA methylation levels (Infinium HumanMethylation450 bead array).Results: We identified and validated 60 unique fusion events in almost half of the analyzed patients (n=69). Of the identified fusion genes, 60% have not previously been reported in ALL or other forms of cancer. The majority of the fusion genes were found in a single patient, but 23% were recurrent, including known ALL fusion genes (n=10) and novel fusion genes (n=7). We found that BCP-ALL samples displayed a higher number of validated fusion genes (54%) compared to the T-ALL samples (28%) moreover in BCP-ALL patients with "other" and "undefined" karyotypes, we detected fusion genes in 71% and 61% of the samples, respectively. High hyperdiploid patients had the lowest rate of validated fusion genes (24%) compared to the other well-known subtypes, where we detected subtype-associated fusion genes in 97% of cases. We also identified promiscuous fusion gene partners, such as ETV6, RUNX1, PAX5 and ZNF384 that fused with up to five different genes. Interestingly, PCA revealed molecularly distinct gene expression and DNA methylation signatures associated with these fusion partners.Conclusion: RNA-sequencing of pediatric ALL cells revealed a detailed view of the heterogeneous fusion gene landscape, identifying both known and novel fusion genes. By grouping samples based on recurrent gene fusion partners we are able to find shared gene expression and DNA methylation patterns compared to other subtypes of ALL, suggesting a shared molecular etiology within these distinct subgroups, offering novel insights into the delineation of fusion genes in ALL. DisclosuresNo relevant conflicts of interest to declare.

Utilization of Mate-Pair Sequencing to Characterize Complex and Novel TCF3 Translocations

Rearrangements involving TCF3 (E2A) at 19p13.3 are a common cytogenetic abnormality in B-lymphoblastic leukemia/lymphoma (B-LL) across all age groups accounting for at least 5% of B-LL. The most common translocation partner, PBX1 at 1q23, is associated with an unbalanced der(19) or a balanced t(1;19) in 80% vs. 20% patients, respectively, and results in a PBX1/TCF3 fusion transcriptional activator. Several other rearrangement partners have been described, and as such TCF3 is approaching the dubious status of a "promiscuous" gene partner. Clinically, our laboratory uses a dual-color, dual fusion PBX1/TCF3 FISH probe to characterize the most common gene fusion; however, this FISH strategy also allows for the identification of atypical disruptions of the TCF3 gene region, and may suggest a gene partner based on abnormal metaphases/metaphase-FISH.Interrogation of our pediatric leukemia database (ages 0-30) identified 219 patients with abnormal TCF3 FISH results. We selected 23 samples for mate-pair evaluation to test the methodology, characterize novel rearrangements and identify new TCF3 fusion partners. In total, 19 patient samples were successfully sequenced by Mate-Pair, including 13 samples with variants of the 1;19 translocation. Of the samples with TCF3/PBX1 fusion, 3 patients demonstrated novel insertional translocation events characterized by mate-pair. A total of 6 samples with undefined/unknown TCF3 partner genes were evaluated. The mate-pair results identified 5 samples with a t(12;19)(p13.31;p13.3), resulting in TCF3/ZNF384 fusion. Interestingly, two of the ZNF384 rearrangements were observed in the unbalanced form, suggesting a similar mechanism related to the der(19)t(1;19) regularly observed in the common PBX1-TCF3 rearrangement. From a karyotype perspective, since these rearrangements result in only a small portion of chromosome 12p translocated onto distal 19p, this rearrangement would "cryptic" by conventional karyotyping. One patient sample demonstrated a new TCF3 gene fusion partner (TEF), associated with a t(19;22)(p13.3;q13.2).Overall, our results demonstrate the utility of mate-pair evaluation as an adjunct methodology in the identification of novel TCF3 rearrangements in B-LL. We have successfully expanded the application of mate-pair to characterize other novel/cryptic abnormalities in various hematologic and oncologic neoplasms encountered in our laboratory. DisclosuresNo relevant conflicts of interest to declare.

NUP98 is rearranged in 3.8% of pediatric AML forming a clinical and molecular homogenous group with a poor prognosis.

Pediatric acute myeloid leukemia (AML) is a rare disease whose prognosis is highly variable according to factors such as chromosomal abnormalities. Recurrent genomic rearrangements are detected in half of pediatric AML by karyotype. NUcleoPorin 98 (NUP98) gene is rearranged with 31 different fusion partner genes. These rearrangements are frequently undetected by conventional cytogenetics, as the NUP98 gene is located at the end of the chromosome 11 short arm (11p15). By screening a series of 574 pediatric AML, we detected a NUP98 rearrangement in 22 cases (3.8%), a frequency similar to CBFB-MYH11 fusion gene (4.0%). The most frequent NUP98 fusion gene partner is NSD1. These cases are homogeneous regarding their biological and clinical characteristics, and associated with bad prognosis only improved by bone marrow transplantation. We detailed the biological characteristics of these AML by exome sequencing which demonstrated few recurrent mutations (FLT3 ITD, WT1, CEBPA, NBPF14, BCR and ODF1). The analysis of the clonal structure in these cases suggests that the mutation order in the NUP98-rearranged pediatric AML begins with the NUP98 rearrangement leading to epigenetic dysregulations then followed by mutations of critical hematopoietic transcription factors and finally, activation of the FLT3 signaling pathway.

Abstract 4371: Integrated molecular characterization of pheochromocytoma and paraganglioma including a novel, recurrent and prognostic fusion gene

Abstract Pheochromocytomas (PCC) and paragangliomas (PGL) are tumors of the autonomic nervous system; 25% are metastatic or locally aggressive. Characterization of the inherited basis of disease has identified a variety of underlying germline mutations; however, understanding of somatic alterations remains limited. As part of The Cancer Genome Atlas, we performed the most comprehensive genomic characterization of PCC/PGL to date, by applying eight genomic profiling assays to 173 patients. Despite having a low overall mutation rate per tumor, we observed remarkable diversity in genomic alterations. 27% of patients had a pathogenic germline mutation among eight known familial PCC/PGL susceptibility genes, thus making PCC/PGL the tumor type with the greatest rate of germline mutations in The Cancer Genome Atlas. 38% of patients possessed a somatic driver mutation across 12 genes. RET, NF1 and VHL were affected by both germline and somatic mutation, albeit with different mutation site tendencies. We identified a new somatic driver gene, CSDE1, which had coordinated intron splicing defects, DNA copy number loss, and RNA under-expression, suggesting a loss of function consequence. Most notably, we discovered the first fusion genes in PCC/PGL from RNA and DNA sequencing (7% of patients), demonstrating for the first time that inter-chromosomal translocation and gene fusion is a method of molecular pathogenesis in this disease. Recurrent, novel MAML3 fusion genes spanned three isoforms and were activating based on over-expression of MAML3 and on fusion transcript exonic expression. MAML3 fusion positive tumors had concomitant dual focal DNA amplification of the fusion gene partners and a significantly divergent methylation profile. Another novel driver gene in PCC/PGL, BRAF, was affected by a hotspot somatic mutation and by an activating fusion gene. Through integrated platform analysis, four statistically significant molecular subtypes of PCC/PGL were detected and found to represent divergent molecular etiology – the kinase signaling subtype, the pseudohypoxia subtype, the Wnt-altered subtype, and the cortical admixture subtype. In particular, MAML3 fusions and CSDE1 mutations defined the new Wnt-altered expression subtype of PCC. Adding to the limited set of prognostic markers in PCC/PGL, three molecular markers were positively associated with clinically aggressive disease: germline mutations in SDHB, somatic mutations in ATRX and fusions involving MAML3. Nearly all somatic driver mutations, germline driver mutations and fusion genes were mutually exclusive across the cohort and covered a large portion of the cohort (69%). Our study provides important novel insights into PCC/PGL biology and identifies potential markers for aggressive disease and therapeutic intervention. Citation Format: Lauren Fishbein, Ignaty Leshchiner, Vonn Walter, Ludmila Danilova, A Gordon Robertson, Amy Johnson, Tara Lichtenberg, Bradley A. Murray, Hanse K. Ghayee, Tobias Else, Shiyun Ling, Stuart R. Jefferys, Aguirre A. de Cubas, Brandon Wenz, Esther Korpershoek, Antonio L. Amelio, Liza Makowski, W Kimryn Rathmell, Anne-Paule Gimenez-Roqueplo, Thomas J. Giordano, Sylvia L. Asa, Arthur S. Tischler, The Cancer Genome Atlas Pheochromocytoma and Paraganglioma Analysis Working Group, Karel Pacak, Katherine L. Nathanson, Matthew D. Wilkerson. Integrated molecular characterization of pheochromocytoma and paraganglioma including a novel, recurrent and prognostic fusion gene. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4371.

Frequency and outcome of pediatric acute lymphoblastic leukemia with ZNF384 gene rearrangements including a novel translocation resulting in an ARID1B/ZNF384 gene fusion.

ZNF384 gene rearrangements with multiple partner genes are recurrent in acute leukemia and are most often associated with a precursor B cell immunophenotype. The overall incidence of this genetic category of leukemia is uncertain. Patients with ZNF384 gene rearrangements from a cohort of 240 precursor B cell acute lymphoblastic leukemia (ALL) pediatric patients over a 3.5-year time period were characterized with detailed cytogenetic, FISH, genomic, and clinical analyses. Seven of the 240 patients were identified to have ZNF384 gene rearrangements including partner genes TCF3 (four patients), EWSR1 (one patient), EP300 (one patient), and the novel gene partner ARID1B (one patient). The translocations were confirmed by FISH analysis and with RNA sequencing for the EP300 and ARID1B partner genes. Genomic microarray analysis showed an average of 2.7 copy number alterations in each case with no evidence of imbalance at the translocation breakpoints. Six of the patients with ZNF384 gene rearrangements had precursor B cell ALL with a CD10- immunophenotype and myeloid-associated antigens. One of the patients also had myeloperoxidase expression and was diagnosed as mixed phenotype B/myeloid acute leukemia. None of the patients have relapsed with event-free survival ranging from 6 years 2 months to 9 years 2 months. This study suggests that the frequency of ZNF384 gene rearrangement in pediatric precursor B cell ALL is approximately 3%. The ARID1B gene, commonly mutated in multiple types of cancer, was identified as an additional ZNF384 gene fusion partner.

Molecular characterization of KMT2A fusion partner genes in 13 cases of pediatric leukemia with complex or cryptic karyotypes.

In pediatric acute leukemias, reciprocal chromosomal translocations frequently cause gene fusions involving the lysine (K)-specific methyltransferase 2A gene (KMT2A, also known as MLL). Specific KMT2A fusion partners are associated with the disease phenotype (lymphoblastic vs. myeloid), and the type of KMT2A rearrangement also has prognostic implications. However, the KMT2A partner gene cannot always be identified by banding karyotyping. We sought to identify such partner genes in 13 cases of childhood leukemia with uninformative karyotypes by combining molecular techniques, including multicolor banding FISH, reverse-transcriptase PCR, and long-distance inverse PCR. Of the KMT2A fusion partner genes, MLLT3 was present in five patients, all with acute lymphoblastic leukemia, MLLT1 in two patients, and MLLT10, MLLT4, MLLT11, and AFF1 in one patient each. Reciprocal reading by long-distance inverse PCR also disclosed KMT2A fusions with PITPNA in one patient, with LOC100132273 in another patient, and with DNA sequences not compatible with any gene in three patients. The most common KMT2A breakpoint region was intron/exon 9 (3/8 patients), followed by intron/exon 11 and 10. Finally, multicolor banding revealed breakpoints in other chromosomes whose biological and prognostic implications remain to be determined. We conclude that the combination of molecular techniques used in this study can efficiently identify KMT2A fusion partners in complex pediatric acute leukemia karyotypes. Copyright © 2016 John Wiley & Sons, Ltd.

TFE3-Fusion Variant Analysis Defines Specific Clinicopathologic Associations Among Xp11 Translocation Cancers.

Xp11 translocation cancers include Xp11 translocation renal cell carcinoma (RCC), Xp11 translocation perivascular epithelioid cell tumor (PEComa), and melanotic Xp11 translocation renal cancer. In Xp11 translocation cancers, oncogenic activation of TFE3 is driven by the fusion of TFE3 with a number of different gene partners; however, the impact of individual fusion variant on specific clinicopathologic features of Xp11 translocation cancers has not been well defined. In this study, we analyze 60 Xp11 translocation cancers by fluorescence in situ hybridization using custom bacterial artificial chromosome probes to establish their TFE3 fusion gene partner. In 5 cases RNA sequencing was also used to further characterize the fusion transcripts. The 60 Xp11 translocation cancers included 47 Xp11 translocation RCC, 8 Xp11 translocation PEComas, and 5 melanotic Xp11 translocation renal cancers. A fusion partner was identified in 53/60 (88%) cases, including 18 SFPQ (PSF), 16 PRCC, 12 ASPSCR1 (ASPL), 6 NONO, and 1 DVL2. We provide the first morphologic description of the NONO-TFE3 RCC, which frequently demonstrates subnuclear vacuoles leading to distinctive suprabasal nuclear palisading. Similar subnuclear vacuolization was also characteristic of SFPQ-TFE3 RCC, creating overlapping features with clear cell papillary RCC. We also describe the first RCC with a DVL2-TFE3 gene fusion, in addition to an extrarenal pigmented PEComa with a NONO-TFE3 gene fusion. Furthermore, among neoplasms with the SFPQ-TFE3, NONO-TFE3, DVL2-TFE3, and ASPL-TFE3 gene fusions, the RCCs are almost always PAX8 positive, cathepsin K negative by immunohistochemistry, whereas the mesenchymal counterparts (Xp11 translocation PEComas, melanotic Xp11 translocation renal cancers, and alveolar soft part sarcoma) are PAX8 negative, cathepsin K positive. These findings support the concept that despite an identical gene fusion, the RCCs are distinct from the corresponding mesenchymal neoplasms, perhaps due to the cellular context in which the translocation occurs. We corroborate prior data showing that the PRCC-TFE3 RCCs are the only known Xp11 translocation RCC molecular subtype that are consistently cathepsin K positive. In summary, our data expand further the clinicopathologic features of cancers with specific TFE3 gene fusions and should allow for more meaningful clinicopathologic associations to be drawn.

Rapid Capture Next-Generation Sequencing in Clinical Diagnostics of Kinase Pathway Aberrations in B-Cell Precursor ALL.

Comprehensive next-generation sequencing (NGS) applications have recently identified various recurrent kinase and cytokine receptor rearrangements in Ph-like B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) amenable to tyrosin kinase inhibitor treatment. For rapid diagnostics of kinase pathway aberrations in minimal residual disease (MRD) high-risk BCP-ALL, we developed a PCR-independent NGS custom enrichment capture panel targeting recurrent genomic alterations, which allows for the identification of unknown 5' fusion partner genes and precise mapping of variable genomic breakpoints. Using a standardized bioinformatics algorithm, we identified kinase and cytokine receptor rearrangements in the majority of ALL patients with high burden of postinduction MRD and enrichment of IKZF1 mutation or deletion (IKZF1(del) ).

Novel PAX3-NCOA1 Fusions in Biphenotypic Sinonasal Sarcoma With Focal Rhabdomyoblastic Differentiation.

Sarcomas arising in the sinonasal region are uncommon and encompass a wide variety of tumor types, including the newly described biphenotypic sinonasal sarcoma (BSNS), which is characterized by a monomorphic spindle cell proliferation with dual neural and myogenic phenotypes. Most BSNSs harbor a pathognomonic PAX3-MAML3 fusion driven by t(2;4)(q35;q31.1), whereas the alternative fusion partner gene remains unidentified in a subset of PAX3-rearranged cases. As NCOA1 on 2p23 is a known partner in PAX3-related fusions in other tumor types (ie, alveolar rhabdomyosarcoma), we investigated its status by fluorescence in situ hybridization (FISH) and reverse transcription polymerase chain reaction assays in 2 BSNS cases showing only PAX3 gene rearrangements. Novel PAX3-NCOA1 fusions were identified in these 2 index cases showing an inv(2)(q35p23) by FISH and confirmed by reverse transcription polymerase chain reaction. Five additional BSNS cases with typical morphology were studied by FISH, revealing a PAX3-MAML3 fusion in 4 cases and only PAX3 rearrangement in the remaining case without abnormalities in MAML3 or NCOA1 gene. Except for 1 case with surface ulceration, all other tumors lacked increased mitotic activity or necrosis, and all cases immunohistochemically coexpressed S100 protein and actin, but lacked SOX10 reactivity. Interestingly, the 2 PAX3-NCOA1-positive cases showed desmin reactivity and displayed a small component of rhabdomyoblastic cells, which were not seen in the more common PAX3-MAML3 fusion cases. In conclusion, we report a novel PAX3-NCOA1 fusion in BSNS, which appears to be associated with focal rhabdomyoblastic differentiation and should be distinguished from PAX3-NCOA1-positive alveolar rhabdomyosarcoma or malignant Triton tumor. SOX10 immunohistochemistry is a useful marker in distinguishing BSNS from peripheral nerve sheath tumors.

Rapid Capture Targeted Next Generation Sequencing (NGS) for Detection of Genomic Kinase- and Cytokine-Receptor Rearrangements in B-Precursor Acute Lymphoblastic Leukemia

Background: Next generation sequencing (NGS) applications have recently identified various recurrent kinase and cytokine receptor rearrangements in a subgroup of B-progenitor acute lymphoblastic leukemia (BPC-ALL) that is characterized by a Ph-like gene expression signature. Implementation of whole genome applications into diagnostics have so far been hampered by high costs and long turnover times. Therefore we developed a custom-made NGS based capture panel without the need for gene specific PCR amplification steps. With a rapid turnover time, pooling of multiple samples and standardized bioinformatics, this approach can be implemented in molecular diagnostics of BCP-ALL to identify patients who may benefit from an add-on therapy with specific tyrosine kinase inhibitors. Moreover, genomic breakpoints can be used as an additional patient specific target for minimal residual disease (MRD) monitoring. Here we report a feasible approach for the identification of kinase and kinase-dependent pathway aberrations in BPC-ALL utilizing a customized sequence enrichment capture panel for NGS.Patients and Methods: Ninety three samples from BCP-ALL patients with detectable minimal residual disease (MRD) levels (≥ 5x10-4) after induction therapy from COALL studies 07-03 or 08-09 were applied to the NGS custom panel. Genomic capture probes were specific for exonic and complete intronic regions of ABL1, JAK2, PDGFRB, CRLF2, EPOR, and for the IgH-JH region on chromosome 14. JAK1, JAK3, IKZF1 and SH2B3 were analysed for exonic mutations only. These predefined genomic regions from recurrently mutated or rearranged kinase and cytokine receptor genes were enriched from 50 ng of initial genomic DNA without gene specific PCR amplification steps, followed by paired end sequencing of the captured genomic fragments (Nextera Rapid Capture Custom enrichment protocol with paired end sequencing on a MiSeq benchtop sequencing platform; Illumina). Six positive controls with known rearrangements (BCR-ABL1 and ID4-JH) were included to verify this method.Results: All breakpoints from 6 positive controls were successfully identified and verified by patient specific amplification of the genomic fusion sites. ABL1 and JH specific capture probes allowed the "fishing" of the genomic fusion partner gene, here BCR and ID4, by paired end sequencing of overlapping, breakpoint spanning reads. In addition we identified a genomic breakpoint for CRLF2, PDGFRB, EPOR, ABL1 and JAK2 in 19/93 BCP-ALL patient samples. One additional patient showed a SH2B3 5 bp insertion in exon 5 that leads to a premature stop codon. The 11 patients with either EBF1-PDGFRB (4), EPOR-JH (4), or CRLF2-JH (3) rearrangements showed the highest levels of MRD (≥ 1x10-2) at the end of induction. MRD monitoring using the genomic breakpoint in 3 cases showed highly concordant data to our standardized IgH/TCR quantification assays. For the 3 patients tested so far, our breakpoint specific MRD assays clearly showed the association of these rearrangements with the dominant leukemic clone.Discussion: In summary, we identified kinase- or cytokine receptor rearrangements in 20/93 patients analyzed with our NGS based custom enrichment panel. The majority of patients had high MRD level at EOI therapy and an age of onset ≥ 10 years. Rapid identification of kinase- or cytokine receptor rearrangements in BCP-ALL is necessary for timely therapeutic intervention with target specific tyrosine kinase inhibitors. Short turnaround times of less than 2 weeks and processing of multiple samples followed by a standardized bioinformatical workflow allows the identification of unknown fusions partners from frequently rearranged kinase- and cytokine receptor genes, providing the exact breakpoint location, irrespective of the gene expression signature. MRD guided NGS panel analysis is a feasible strategy for identification of patients with a high risk of therapeutic failure or relapse suitable for targeted TKI intervention. Table 1Age at DxFusionMRD at EOI13EBF1-PDGFRB1,0E+009EBF1-PDGFRB9,0E-0113EBF1-PDGFRB3,0E-019EBF1-PDGFRB7,0E-0216EPOR-IGH6,0E-017EPOR-IGH3,0E-0116EPOR-IGH1,0E-0118EPOR-IGH9,0E-0211CRLF2-IGH9,0E-0211CRLF2-IGH4,7E-0216CRLF2-IGH4,0E-0215PAX5-JAK27,0E-0411RCSD1-ABL15,0E-0210SH2B3-INS3,0E-0310PAR15,0E-0110PAR17,0E-021PAR11,8E-025PAR17,0E-038PAR12,0E-032,5PAR11,5E-03 DisclosuresNo relevant conflicts of interest to declare.

Fusion Gene Detection Using Whole Transcriptome Analysis in Patients with Chronic Myeloproliferative Neoplasms and Secondary Acute Myeloid Leukemia

Fusion oncogenes resulting from chromosomal aberrations are common disease drivers in myeloid malignancies. The most prominent example is BCR-ABL1 fusion present in chronic myeloid leukemia, which together with essential thromobocythemia (ET), primary myelofibrosis (PMF) and polycythemia vera (PV) belongs to the classic myeloproliferative neoplasms (MPN). The BCR-ABL1 negative MPNs are driven by somatic mutations in JAK2, MPL and CALR. MPN patients can progress to acute myeloid leukemia (AML) but the transformation process is not well understood. Studies using standard karyotyping and SNP microarrays have shown that disease progression is characterized by an increase in karyotype complexity. We aimed to identify novel fusion oncogenes in patients with BCR-ABL1 negative MPN during chronic phase and disease progression in high-throughput and cost-efficient manner using RNA-seq technology. In addition this approach enabled us to perform RNA-seq variant calling for identification of gene mutations on the same cohort of patients.Whole transcriptome sequencing was performed on 121 patients (112 chronic phase MPN and 9 secondary AML samples) and 23 healthy controls in a 100 base pair paired-end manner. The cohort consisted of 44% PMF, 22% ET, 12% PV and 6% secondary AML patients. The output of three fusion detection tools (Defuse, Tophat-fusion and SOAPfuse) was combined in order to increase sensitivity. Extensive filtering steps were applied in order to enrich for cancer specific fusion events, including filtering for fusions appearing in healthy individuals, filtering for read-throughs and false positives with external databases and manual inspection of sequencing reads. The outcome of analysis for Defuse, Tophat-fusion and SOAPfuse resulted in the total of 52, 54 and 38 candidate fusions, respectively. Candidate fusions were Sanger-sequenced and for Tophat-fusion and Defuse the validation rate was 60%, while for SOAPfuse only 20% could be validated. Approximately 70% of the fusion candidates were not shared among the 3 tools which underlines the importance of selecting the union of all calls from each tool rather than the intersect.We did not observe clustering of breakpoints along the genome. Most fusion candidates could be detected in PMF which corresponds to the disease entity that was most represented in the cohort (44% of patients). No enrichment for fusions was found in 7 triple negative (no JAK2, CALR, MPL mutations) cases. 42% of chromosomal aberrations were translocations, followed by duplication (31%), inversion (14%) and deletion events (11%). Among the intragenic fusions, approximately half had genomic breakpoints less than 1 Mb apart. 70% of validated fusions were out of frame, while 28% were in frame. In the leukemic samples a higher abundance of fusions was found (4/9). Typical fusions for de novo AML were not detected within secondary AML (sAML) samples. We did not detect a recurrent fusion oncogene in our patient cohort.In a PMF patient with JAK2-V617F mutation we identified a BCR-ABL1 fusion, indicating a clonal exchange which was consistent with patient's phenotype. Another PMF patient exhibited an inversion event involving the first exon of CUX1, causing a CUX1 loss of function. Other fusions in chronic MPN patients affected genes involved in histone modifications (SMYD3-AHCTF1, KDM4B-CYHR1). In post-MPN AML patients we identified a somatic in frame-fusion involving INO80D and GPR1 and a fusion truncating the first 3 exons of RUNX2 (XPO5-RUNX2).The high quality of RNA sequencing data, allowed us to set up a variant detection workflow that will be compared with matched samples that have been exome sequenced. Preliminary results could demonstrate that mutations in the JAK2 gene in a cohort of 96 patients were all correctly recalled, emphasizing its sensitivity.Fusion events among patients in chronic phase MPN are rare and the majority of these events imply loss of function of both fusion gene partners. This approach adds valuable information on the true frequency of inactivation of genes such as CUX1 in patients, as small inversions like the one described above would not be detectable by other methods. Detection of a subclone with BCR-ABL1 fusion underlines the strength of the fusion detection workflow for diagnostic purposes. Typical de novo AML fusions were not found in sAML and further suggests that de novo AML and sAML are distinct disease entities on a genetic level. DisclosuresGisslinger:Janssen Cilag: Honoraria, Speakers Bureau; Sanofi Aventis: Consultancy; AOP ORPHAN: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; Geron: Consultancy. Kralovics:AOP Orphan: Research Funding; Qiagen: Membership on an entity's Board of Directors or advisory committees.

Abstract A75: Pan-cancer identification of fusion genes as therapeutic targets in cancer

Abstract Fusion genes are a well established category of oncogenic mutations, in which a chromosomal rearrangement brings together parts of two different genes to create a novel gene with oncogenic potential. Originally identified mostly in hematologic malignancies (e.g. BCR-ABL1 in CML), over the last years fusion genes have been shown to occur in practically all types of cancers examined. Some of the best known examples of these are ETS-family gene fusions (e.g. TMPRSS2-ERG) in prostate cancer and EML4-ALK fusions in non-small cell lung cancer. Although the prevalence of a specific gene fusion in a single cancer is often low, the example of treating e.g. EML4-ALK fusion positive NSCLC cancers with ALK inhibitors, such as crizotinib and ceritinib, has shown gene fusions to have significant value as targets of drug development. In this study, we describe a comprehensive survey of gene fusions in 7428 cancer samples from 27 different cancer types, using paired-end RNA-seq data created by the TCGA project. At least one fusion gene was identified in 3801/7428 samples, with over 9000 genes taking part in a total of ∼11000 fusion gene events. The number of gene fusions per tumor is highly variable, with the largest number of fusions typically identified in tumors with high level amplifications. This suggests many of the fusion genes identified here may arise as byproducts of amplicon formation, making them likely passenger events. Several potentially targetable genes take part in gene fusions across different cancer types. For instance, we identified a total of 12 gene fusions involving ALK in 5 different cancer types. Strikingly, only 5 of these involve EML4 as 5' partner gene. NTRK fusions were identified in 24 samples from 9 cancer types, FGFR fusions in 39 samples from 14 cancer types and MAST family kinase fusions in 14 samples from 7 cancer types. In summary, our analysis of fusion gene occurrence across a wide variety of cancer types identifies several interesting and potentially targetable gene fusions. Furthermore, it illustrates that many of these are found across several different cancer types, as well as involve a large number of different fusion partner genes, suggesting this may need to be taken into account in diagnostics of fusion genes as well as selection of patients for clinical trials. Citation Format: Henrik Edgren, Kalle Ojala, Anja Ruusulehto. Pan-cancer identification of fusion genes as therapeutic targets in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A75.

Wnt signaling induces transcription, spatial proximity, and translocation of fusion gene partners in human hematopoietic cells

AbstractChromosomal translocations are frequently associated with a wide variety of cancers, particularly hematologic malignancies. A recurrent chromosomal abnormality in acute myeloid leukemia is the reciprocal translocation t(8;21) that fuses RUNX1 and ETO genes. We report here that Wnt/β-catenin signaling increases the expression of ETO and RUNX1 genes in human hematopoietic progenitors. We found that β-catenin is rapidly recruited into RNA polymerase II transcription factories (RNAPII-Ser5) and that ETO and RUNX1 genes are brought into close spatial proximity upon Wnt3a induction. Notably, long-term treatment of cells with Wnt3a induces the generation a frequent RUNX1-ETO translocation event. Thus, Wnt/β-catenin signaling induces transcription and translocation of RUNX1 and ETO fusion gene partners, opening a novel window to understand the onset/development of leukemia.

Hematolymphoid neoplasms associated with rearrangements of PDGFRA, PDGFRB, and FGFR1.

This session of the 2013 Society for Hematopathology/European Association for Haematopathology Workshop was dedicated to tumors currently included in the World Health Organization (WHO) classification category of myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, and FGFR1. We use the cases submitted to this session to review the clinicopathologic and genetic spectrum of these neoplasms, methods for their diagnosis, and issues related to the WHO classification terminology. Since many patients with these neoplasms have eosinophilia, we also briefly mention other causes of clonal eosinophilia. These neoplasms are the result of gene fusions involving any one of these three tyrosine kinase genes. A variety of gene fusion partners have been found consistently for each category of neoplasms. Diagnoses of these neoplasms are often highly challenging and require a high index of suspicion and a multidisciplinary approach. Early recognition of these neoplasms is important because patients with neoplasms associated with PDGFRA or PDGFRB fusions often respond to tyrosine kinase inhibitor therapy, whereas patients with neoplasms associated with FGFR1 fusions usually do not respond.

Abstract 3389: A multiplexed immunohistochemistry test to screen for protein overexpression of ROS1, TrkA, TrkB and TrkC in multiple tumor tissue types

Abstract Introduction: A consequence of precision medicine is the increased challenge to identify small patient populations, while maintaining testing efficiency and manageable costs. One area of focus is identifying gene rearrangements in patients for targeted kinase inhibitor therapies, where the prevalence in a patient population can be ∼1-10%. Diagnostic detection of gene rearrangements is primarily accomplished by fluorescence in situ hybridization (FISH), while next generation sequencing (NGS) or immunohistochemistry (IHC) show promise. FISH does not provide information regarding the gene fusion partner, while NGS is expensive and labor intensive. IHC is both high throughput and cost efficient, but not specific to rearrangements. To enable rapid screening of large tissue populations for prevalence, we sought to develop a method that could be broadly applied to multiple receptor tyrosine kinases simultaneously to streamline screening for multi-targeted therapeutics. To this end, we have developed a multiplexed IHC method that assesses expression of the clinically promising markers: ROS1, TrkA, TrkB, and TrkC in multiple tumor tissues. Specimens selected positive by this pan-receptor IHC assay can then be reflexed to a method with higher sensitivity and specificity for gene rearrangements (e.g. NGS). Methods: Standard IHC was conducted as follows: Antigen retrieval was performed in EDTA (pH 9) at 98°C for 30 min. The primary antibody cocktail consists of antibodies against ROS1 (D4D6, Cell Signaling) and a pan-Trk antibody (C17F1, Cell Signaling). A signal amplification step was performed before the secondary antibody conjugated to a dextran-HRP polymer (Envision FLEX, Dako) step. Signal was developed using DAB and counterstained with hematoxylin. Results: We have developed an assay for measuring expression of multiple receptor tyrosine kinases in multiple tissue types using a cocktail of antibodies that is sensitive, accurate, and with minimal background or cross-reactive staining. This has been demonstrated using characterized cell lines and human tissues with results confirmed by testing individual IHC markers and alternative methods (e.g. FISH or NGS). Since IHC measurements are assessing in-frame expression, we can also identify false positive samples such as FISH detected rearrangements which do not lead to active protein product. Conclusions: We have demonstrated a simple, sensitive, multiplexed IHC assay to screen for molecular alterations (ROS1, TrkA/B/C) that are currently not part of standard tissue annotation. We have shown that the assay is able to identify molecular alterations that have been confirmed by sequencing. The test is expandable and can be adjusted to suit the needs of researchers studying specific protein families. Citation Format: Aaron Boomer, Diane Fernandez, Danielle Murphy, Jason Christiansen, Jennifer Lamoureux. A multiplexed immunohistochemistry test to screen for protein overexpression of ROS1, TrkA, TrkB and TrkC in multiple tumor tissue types. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3389. doi:10.1158/1538-7445.AM2015-3389

Novel FUS-KLF17 and EWSR1-KLF17 fusions in myoepithelial tumors.

Myoepithelial (ME) tumors of soft tissue and bone display a heterogeneous histologic spectrum and in about half of the cases harbor EWSR1 gene rearrangements. Despite rare case reports, the prevalence of fused in sarcoma (FUS) gene abnormalities and its related fusion partners remains undetermined among ME tumors. Therefore, we screened 66 EWSR1-negative ME tumors for FUS abnormalities by fluorescence in situ hybridization (FISH). In an index FUS-rearranged case, 3'-rapid amplification of cDNA ends (RACE) was applied to identify the fusion partner. Results were further confirmed by reverse transcription-PCR, followed by FISH screening the entire cohort of FUS-rearranged and EWSR1-positive ME lesions lacking a known fusion partner. The correlation between genotype and clinicopathological features was also investigated. As a result, six (9%) FUS-rearranged cases were identified, spanning divergent age groups, tumor locations, and morphologic features. A novel FUS-KLF17 fusion was identified by 3'-RACE in an 11-year-old girl with a foot lesion associated with locoregional metastases. Three additional cases with FUS-KLF17 fusions were identified and one KLF17 rearrangement (6.3%) was found among the 16 EWSR1-positive cases tested. The KLF17-related ME tumors affected younger patients and often exhibited trabecular growth in a myxohyaline stroma, but this genotype did not correlate with a malignant phenotype. In conclusion, a small subset of ME tumors harbor FUS rearrangements, two thirds of them being associated with KLF17 fusion. FUS FISH analysis is recommended in EWSR1-negative lesions in which a ME diagnosis is suspected. KLF17 is also a rare gene fusion partner to EWSR1-rearranged ME tumors.

The Structural Characterization of Tumor Fusion Genes and Proteins.

Chromosomal translocation, which generates fusion proteins in blood tumor or solid tumor, is considered as one of the major causes leading to cancer. Recent studies suggested that the disordered fragments in a fusion protein might contribute to its carcinogenicity. Here, we investigated the sequence feature near the breakpoints in the fusion partner genes, the structure features of breakpoints in fusion proteins, and the posttranslational modification preference in the fusion proteins. Results show that the breakpoints in the fusion partner genes have both sequence preference and structural preference. At the sequence level, nucleotide combination AG is preferred before the breakpoint and GG is preferred at the breakpoint. At the structural level, the breakpoints in the fusion proteins prefer to be located in the disordered regions. Further analysis suggests the phosphorylation sites at serine, threonine, and the methylation sites at arginine are enriched in disordered regions of the fusion proteins. Using EML4-ALK as an example, we further explained how the fusion protein leads to the protein disorder and contributes to its carcinogenicity. The sequence and structural features of the fusion proteins may help the scientific community to predict novel breakpoints in fusion genes and better understand the structure and function of fusion proteins.

RCSD1-ABL1 Translocation Associated with IKZF1 Gene Deletion in B-Cell Acute Lymphoblastic Leukemia.

The RCSD1 gene has recently been identified as a novel gene fusion partner of the ABL1 gene in cases of B-cell Acute Lymphoblastic Leukemia (B-ALL). The RCSD1 gene is located at 1q23 and ABL1 is located at 9q34, so that the RCSD1-ABL1 fusion typically arises through a rare reciprocal translocation t(1;9)(q23;q34). Only a small number of RCSD1-ABL1 positive cases of B-ALL have been described in the literature, and the full spectrum of clinical, morphological, immunophenotypic, and molecular features associated with this genetic abnormality has not been defined. We describe extensive genetic characterization of a case of B-ALL with RCSD1-ABL1 fusion, by using conventional cytogenetic analysis, Fluorescence In Situ Hybridization (FISH) studies, and Chromosomal Microarray Analysis (CMA). The use of CMA resulted in detection of an approximately 70 kb deletion at 7p12.2, which caused a disruption of the IKZF1 gene. Deletions and mutations of IKZF1 are recurring abnormalities in B-ALL and are associated with a poor prognosis. Our findings highlight the association of the deletion of IKZF1 gene with the t(1;9)(q24;q34) and illustrate the importance of comprehensive cytogenetic and molecular evaluation for accurate prediction of prognosis in patients with B-cell ALL.

Big genes are big mutagen targets: A connection to cancerous, spherical cells?

We determined the most commonly mutated genes in five cancer genome atlas (TCGA) datasets. Many of these genes were extraordinarily large, as are many cancer fusion gene partners. And many of these genes had cytoskeletal related functions. We further determined that these genes were distributed into high and low frequency mutation groups largely according to overall rate of gene-occurrence in the high and low mutation frequency groups, as was also the case with common metastasis and tumor suppressor genes. Oncoproteins were selectively mutated in the low mutation frequency groups in colon and lung datasets. Thus, genes that have very large coding regions and may impact the cytoskeleton are more commonly mutated than are common metastasis and tumor suppressor genes in both high and low frequency mutation groups. These analyses raise questions related to cell shape: (i) Are cancer cells often spherical because cytoskeletal-related proteins are large mutagen targets? (ii) Is drug-resistance facilitated by relatively common mutant proteins that lead to round cells, with altered cell physiology or reduced surface to volume ratios that could reduce intra-cellular drug concentrations?

Abstract 4668: A next generation sequencing assay to detect the fusion products of ALK, ROS1 and RET with any fusion partner genes and hotspot mutations in FFPE samples

Abstract Targeted drugs have been widely used in the treatment of lung cancer, especially for non small cell lung cancer (NSCLC) patients. NCCN guideline lists multiple drugs which are particularly effective in the subgroup of patients with specific gene mutation variants, including the fusion transcripts of ALK, ROS1 and RET, and the mutations of EGFR, KRAS, BRAF and HER2. Multiple techniques have been developed to detect fusion transcripts in tumor samples, such as FISH, IHC and PCR assays. FISH is the most accurate method for fusion detection currently. The split probe FISH assay, which does not require the pre-knowledge of what is the fusion partner with ALK for example, can detect unknown ALK fusion products as well. However, it fails to identify which gene is fused with ALK (or other oncogene) in the chimera products, therefore is not informative for the mechanism or drug resistance study. In addition, due to the limitation on the fluoresce dye, it is quite difficult to multiplex fusion FISH probes for different genes into one assay. We describe here a next generation sequencing assay to detect a panel of fusion transcripts and mutations in one single assay. Our single assay can detect the fusion products of ALK, ROS1 and RET with any known or unknown fusion partners, together with the hotspot mutations in EGFR, KRAS, BRAF and HER2. Our assay can identify not only the exact sequence of the unknown fusion partners, but also any mutations within the full coding regions of ALK, ROS1 and RET. This information is critical for the resistance mechanism study and the next generation inhibitor drug development, since about half of the ALK inhibitor resistance was caused by the mutations in ALK gene itself. We have identified a novel ALK fusion gene with a never-reported fusion partner in a lung cancer patient. The xenograft model derived from this patient responds to crizotinib well in the in vivo study (published on Journal of Thoracic Oncology). We have demonstrated that our assay can reliably detect both the novel fusion and the well known EML4-ALK fusion from only 1-2 5um FFPE slides of the lung tumor tissues, together with other possible fusions and mutations as well. Note: This abstract was not presented at the meeting. Citation Format: Qiang Xu, Guan Wang, Bo Li, Maoxiang Qian, Douglas Fang, Lele Sun, Yundi Chen, Hongye Sun. A next generation sequencing assay to detect the fusion products of ALK, ROS1 and RET with any fusion partner genes and hotspot mutations in FFPE samples. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4668. doi:10.1158/1538-7445.AM2014-4668