1p Deletions Research Articles

Histopathological grading affects survival in patients with IDH-mutant grade II and grade III diffuse gliomas

BackgroundDiffuse grade II and grade III gliomas are actually classified in accordance with the presence of isocitrate dehydrogenase mutation (IDH-mut) and the deletion of both 1p and 19q chromosome arms (1p/19q codel). The role of tumour grading as independent prognostic factor in these group of tumours remains matter of debate. The aim of this study was to determine if grade is an independent prognostic factor and not somehow associated to IDH mutation and 1p/19q status of the tumour. MethodsWe analysed 399 consecutive patients with newly diagnosed, histologically proven World Health Organisation (WHO) 2016 grade II or grade III IDH-mut gliomas, assessed by polymerase chain reaction, immunohistochemistry or next-generation sequencing (NGS). ResultsThe analysis included 399 patients with grade II (n = 250, 62.7%) or grade III (n = 149, 37.3%) diffuse gliomas. Median follow-up time was 105.3 months. Median survival was 148.1 months. In multivariate analysis, grade II (hazard ratio [HR] = 0.342, 95% confidence interval [CI]: 0.221–0.531; P < 0.001) and 1p/19q codeletion (HR = 0.440, 95% CI: 0.290–0.668; P < 0.001) were independently associated with a lower risk for death. The difference in survival remained significant (p = 0.006 in astrocytomas, p = 0.014 in oligodendrogliomas) when adjusted for histological subtype. Residual disease after surgery (or biopsy) negatively affected survival (HR: 2.151, 95% CI: 1.375–3.367, P = 0.001). Post-surgical treatment with radiotherapy + adjuvant chemotherapy improved survival compared with follow-up and other treatments (HR: 0.316, 95% CI: 0.156–0.641, P = 0.001). ConclusionsIn our study, histopathological grade still affects survival in IDH-mutant WHO grade II and III diffuse gliomas. This effect appears to be independent from molecular features, extension of surgical resection and post-surgical treatments. Therefore, physicians should continue to take into account tumour grade, along their molecular characteristics, for a better clinical and therapeutic management of the patients.

Abstract B30: ARID1A is a haploinsufficient tumor suppressor for N-Myc transformation of neural crest cells

Abstract Large segmental chromosomal alterations are common to cancer and a feature of high-risk neuroblastoma (NBL). Though they are early or initiating events in cancer, including often being found in precancerous lesions, their contribution to tumorigenesis is poorly understood. An unproven model is that these changes promote cancer through the cumulative effect of multiple dosage-sensitive genes. Loss of heterozygosity (LOH) at 1p36 is a frequent structural rearrangement in a broad range of human cancers including NBL. Approximately 70% of MYCN amplified NBL have 1p36 LOH with both mutations independently contributing to tumor aggressiveness in NBL. Two tumor suppressor regions have been proposed to exist in 1p36, a distal and proximal region, which have MYCN-independent and dependent roles. Through CRISPR/Cas9 genome editing of primary mouse neural crest cells (NCCs), a source for NBL, we found that loss of the chromatin remodeling factor Chd5 conferred most of the tumor-suppressor effects of 1p36 LOH in in vitro cell transformation assays in cells with endogenous levels of N-Myc. In contrast, when N-Myc was overexpressed, tumor evolution of NCCs genome edited to have randomly sized 1p36 deletions showed a reduction in tumor latency that significantly correlated with deletion of Arid1a. The Arid1a deletions that were selected for ranged from small indels up to large 1p36 deletions, indicating that large deletions are tolerated to achieve loss of a single critical tumor suppressor. Further, using lentiviral Cre-induced deletion of floxed Arid1a in isolated NCCs, we found that Arid1a is a haploinsufficient tumor suppressor in MYCN-driven transformation of NCCs. As Arid1a is a subunit of the chromatin remodeling complex SWI/SNF, which is mutated in 20% of cancers, Arid1a synthetic lethal therapies are being developed for adult malignancies. We are currently verifying those proposed therapies in NBL and are using small-molecule screening of cells lines derived from Arid1a wild-type, het, or null tumors to identify additional synthetic lethalities. Our findings indicate that context, such as the status of MYCN as an oncogene, dictates which 1p36 gene is the critical tumor suppressor, establishing 1p36 LOH as multifaceted not cumulative, as was previously believed. Citation Format: Kirby Wallace, Jesus Garcia-Lopez, Joel Otero, Rachelle Olsen, Chelsea DeVaux, Ashton King, Andrew Davidoff, Kevin Freeman. ARID1A is a haploinsufficient tumor suppressor for N-Myc transformation of neural crest cells [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B30.

Genetic landscape of external auditory canal squamous cell carcinoma.

External auditory canal squamous cell carcinoma (EACSCC) is an extremely rare and aggressive malignancy. Due to its rarity, the molecular and genetic characteristics of EACSCC have not yet been elucidated. To reveal the genetic alterations of EACSCC, we performed whole exome sequencing (WES) on 11 primary tumors, 1 relapsed tumor and 10 noncancerous tissues from 10 patients with EACSCC, including 1 with a rare case of synchronous bilateral EACSCC of both ears. WES of the primary tumor samples showed that the most frequently mutated gene is TP53 (63.6%). In addition, recurrent mutations in CDKN2A, NOTCH1, NOTCH2, FAT1 and FAT3 were detected in multiple samples. The mutational signature analysis of primary tumors indicated that the mutational processes associated with the activation of apolipoprotein B mRNA‐editing enzyme catalytic polypeptide‐like (APOBEC) deaminases are the most common in EACSCC, suggesting its similarity to SCC from other primary sites. Analysis of arm‐level copy number alterations detected notable amplification of chromosomes 3q, 5p and 8q as well as deletion of 3p across multiple samples. Focal chromosomal aberrations included amplifications of 5p15.33 (ZDHHC11B) and 7p14.1 (TARP) as well as deletion of 9p21.3 (CDKN2A/B). The protein expression levels of ZDHHC11B and TARP in EACSCC tissues were validated by immunohistochemistry. Moreover, WES of the primary and relapsed tumors from a case of synchronous bilateral EACSCC showed the intrapatient genetic heterogeneity of EACSCC. In summary, this study provides the first evidence for genetic alterations of EACSCC. Our findings suggest that EACSCC mostly resembles other SCC.

Genomic testing and counseling: The contribution of next-generation sequencing to epilepsy genetics.

Currently, next-generation sequencing (NGS) technology is more accessible and available to detect the genetic causation of diseases. Though NGS technology benefited some clinical phenotypes, for some clinical diagnoses such as seizures and epileptic disorders, adaptation occurred slowly. The genetic diagnosis was mainly based on epilepsy gene panels and not on whole exome and/or genome sequencing. We retrospectively analyzed 420 index cases, referred for NGS over a period of 18 months, to investigate the challenges in diagnosing epilepsy. Of the 420 cases, 65 (15%) were referred due to epilepsy with one third having a positive family history. The result of the NGS was 14 positive cases (21.5%), 16 inconclusive cases (24%), and 35 (53%) negative cases. No gene has been detected twice in the inconclusive and positive groups. Comparative genomic hybridization has been performed for all 30 NGS negative cases and four cases with pathogenic variants (deletion in 15q11.213.1, deletion of 2p16.3, deletion in Xq22.1, and deletion in 17p13.3) were identified. These findings have implications for our understanding of the approach to genetic testing and counseling of patients affected with seizures and epilepsy disorders. The overall diagnostic yield of exome/genome sequencing in our cohort was 23%. The main characteristic is genetic heterogeneity, supporting NGS technology as a suitable testing approach for seizures and epilepsy disorders. Genetic counseling for newly identified disease-causing variants depends on the pedigree interpretation, within the context of disease penetrance and variable expressivity.

Up regulation of the Hippo signalling effector YAP1 is linked to early biochemical recurrence in prostate cancers

The transcriptional coactivator YAP1 controls the balance between cell proliferation and apoptosis. YAP1 overexpression is linked to poor prognosis in many cancer types, yet its role in prostate cancer is unknown. Here, we applied YAP1 immunohistochemistry to a tissue microarray containing 17,747 clinical prostate cancer specimens. Cytoplasmic and nuclear YAP1 staining was seen in 81% and 63% of tumours. For both cytoplasmic and nuclear YAP1 staining, high levels were associated with advanced tumour stage, classical and quantitative Gleason grade, positive nodal stage, positive surgical margin, high KI67 labelling index, and early biochemical recurrence (p < 0.0001 each). The prognostic role of YAP1 staining was independent of established prognostic features in multivariate models (p < 0.001). Comparison with previously studied molecular markers identified associations between high YAP1 staining, TMPRSS2:ERG fusion (p < 0.0001), high androgen receptor (AR) expression (p < 0.0001), high Ki67 labelling index (p < 0.0001), and PTEN and 8p deletions (p < 0.0001 each). In conclusion, high YAP1 protein expression is an independent predictor of unfavourable disease course in prostate cancer. That cytoplasmic and nuclear YAP1 staining is equally linked to phenotype and prognosis fits well to a model where YAP1 activation during tumour progression includes up regulation, cytoplasmic accumulation and subsequent translocation to the nucleus.

Abstract A44: Functional models of chromosome arm-level aneuploidies in cancer

Abstract Aneuploidy, whole-chromosome or chromosome arm copy number imbalance, is a near-universal characteristic of human cancers. We previously applied methods that define chromosome arm-level aneuploidy and a global cancer aneuploidy score to 10,522 tumors of 33 types in The Cancer Genome Atlas (TCGA). Aneuploidy level was correlated with TP53 mutation, somatic mutation rate, and expression of proliferation genes. Overall aneuploidy was anti-correlated with expression of immune signaling genes, due to decreased leukocyte infiltrates in high-aneuploidy samples. In contrast, some individual chromosome arm alterations correlated with higher expression of immune signaling genes, including deletion of chromosome 3p, 8p, and 17p. Cancer subtypes are often characterized by tumor specific patterns of arm-level copy number alterations; for example, squamous cell carcinomas (SCCs) from different tissues of origin (including lung, esophagus, and bladder) have a pattern of chromosome 3p loss and chromosome 3q gain. Although yeast and mammalian models of whole-chromosome aneuploidies have been extensively investigated, chromosome arm-level aneuploidies have rarely been modeled. However, recent advances in genome engineering and targeting of endonucleases allow generation of large chromosomal alterations. We used the CRISPR-Cas9 system to delete one copy of chromosome 3p in human immortalized lung epithelial cells, validated in 8 clones by whole-genome sequencing. Consistent with patient data, expression of 3p genes was decreased upon deletion, as well as increased expression of interferon response genes. Phenotypic characterization revealed that cells with chromosome 3p deletion initially proliferated more slowly than their siblings. These chromosome 3p-deleted cells had increased G1 arrest but did not undergo increased apoptosis or cell death. Interestingly, after several passages in culture, the proliferation defect was rescued in chromosome 3p-deleted cells; genome sequencing and karyotype analyses suggested that this was partially the result of chromosome 3 duplication. With our cellular model of chromosome arm-level aneuploidy, we uncovered a selection mechanism that allowed aneuploidy tolerance in vitro. We have also grown these cells in spheroid and organoid culture systems to assess the effects of chromosome 3 arm-level aneuploidies on cytokine production and squamous differentiation and are using these systems to identify how chromosome 3p deletion affects drug sensitivity. In conclusion, our genome engineering approach to model chromosome arm-level deletions provides a robust model that will address a gap in our understanding of aneuploidy in cancer. Citation Format: Alison M. Taylor, Sejal Jain, Juliann Shih, Andrew D. Cherniack, Rameen Beroukhim, Matthew Meyerson. Functional models of chromosome arm-level aneuploidies in cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A44.

Application of Next-Generation Sequencing for the Genomic Characterization of Patients with Smoldering Myeloma

Genomic analysis could contribute to a better understanding of the biological determinants of the evolution of multiple myeloma (MM) precursor disease and an improved definition of high-risk patients. To assess the feasibility and value of next-generation sequencing approaches in an asymptomatic setting, we performed a targeted gene mutation analysis and a genome-wide assessment of copy number alterations (CNAs) by ultra-low-pass whole genome sequencing (ULP-WGS) in six patients with monoclonal gammopathy of undetermined significance and 25 patients with smoldering MM (SMM). Our comprehensive genomic characterization highlighted heterogeneous but substantial values of the tumor fraction, especially in SMM; a rather high degree of genomic complexity, in terms of both mutations and CNAs, and inter-patient variability; a higher incidence of gene mutations and CNAs in SMM, confirming ongoing evolution; intraclonal heterogeneity; and instances of convergent evolution. ULP-WGS of these patients proved effective in revealing the marked genome-wide level of their CNAs, most of which are not routinely investigated. Finally, the analysis of our small SMM cohort suggested that chr(8p) deletions, the DNA tumor fraction, and the number of alterations may have clinical relevance in the progression to overt MM. Although validation in larger series is mandatory, these findings highlight the promising impact of genomic approaches in the clinical management of SMM.

MON-LB48 The Genomic Landscape of Sporadic Thyrotrophinomas

Background: Thyrotrophinoma (TSHoma) is rare and knowledge on the genomic landscape of this tumour type is very limited. Aim: To perform whole-exome sequencing (WES) in a population of TSHomas to identify recurrent somatic genetic events Method: WES was performed on paired tumour and germline DNA of 7 patients with TSHomas. Three tissue samples were formalin-fixed paraffin-embedded and 4 fresh frozen tumour samples. Fresh blood samples were also collected from each patient. The average of mean depth of coverage amongst all samples was 129X, and 97% of target bases were covered ≥20X. Results:Four (57%) of the seven patients were male and median age at diagnosis was 52 years. (IQR 46, 60) Six patients (86%) had macroadenomas. Four patients (57%) had central thyrotoxicosis at diagnosis and three patients’ tumour stained positive for TSH on histology examination. Two patients (29%) had growth hormone co-secreting tumours. In total, 69 somatic variants were identified to be of potential interest, averaging 1.4 variants per million base-pair of DNA read. No variants were observed in more than one individual. According to the GTEx database, 9 of 69 genes (DRC3, HDAC5, KDM1A, POLR21, TCF25, THAP7, TTC13, UNC5D, UNC13A) were highly expressed in the pituitary (top 10%). Four of these genes appear to contribute to tumour development via epigenetic pathway. Specifically, three of these genes (HDAC5, KDM1A, THAP7) either interact with or form part of histone deacetylases whilst POLR21 encodes a subunit of RNA polymerase II which is responsible for mRNA synthesis. On the other hand, TCF25 gene is thought to act as transcriptional repressor and UNC5D plays a role in cell-cell adhesion.Large scale copy number variations involving gain or loss of whole chromosome or chromosome (chr) arm were observed in six (86%) tumour samples. Chr 5, 9, 13 and 19 were most commonly affected by chromosomal gains. Deletion of chr 1p was seen in two cases and mutations in KDM1A (p.Glu161fs/c.482_491delAGGAAGAAAA) and ADGRB2 gene (p.Leu1565Gln/c.4694T>A) were found in each of the remaining single copy of chr 1p. ADGRB2 gene is thought to be involved in cell adhesion and angiogenesis inhibition. Copy neutral loss-of-heterozygosity were present in two (29%) of the tumour samples (chr 2 and 12q). However, no somatic mutation was found in these regions. Gene level copy number analysis identified a potential deletion in TTI2 gene which encodes for a regulator in DNA damaging response as well as telomere length regulation. ConclusionOverall, the rate of somatic variant mutations in TSHomas is low, consistent with the relative benign nature of this tumour type. No classical driver mutations were identified by this study however, chromosomal anomalies and epigenetics may play an important part in TSHoma development.

Gene signatures associated with genomic aberrations predict prognosis in neuroblastoma.

BackgroundNeuroblastoma (NB) is a heterogeneous disease with respect to genomic abnormalities and clinical behaviors. Despite recent advances in our understanding of the association between the genetic aberrations and clinical features, it remains one of the major challenges to predict prognosis and stratify patients for determining personalized therapy in this disease. The aim of this study was to develop an effective prognosis prediction model for NB patients.MethodsWe integrated diverse computational analyses to define gene signatures that reflect MYCN activity and chromosomal aberrations including deletion of chromosome 1p (Chr1p_del) and chromosome 11q (Chr11q_del) as well as chromosome 11q whole loss (Chr11q_wls). We evaluated the prognostic and predictive values of these signatures in seven NB gene expression datasets (the number of samples ranges from 94 to 498, with a total of 2120) generated from both RNA sequencing and microarray platforms.ResultsMYCN signature was a more effective prognostic marker than MYCN amplification status and MYCN expression. Similarly, the Chr1p_del score was more prognostic than Chr1p status. The activity scores of MYCN, Chr1p_del and Chr11q_del were associated with poor prognosis, while the Chr11q_wls score was linked to good outcome. We integrated the activity scores of MYCN, Chr1p_del, Chr11q_del, and Chr11q_wls and clinical variables into an integrative prognostic model, which displayed significant performance over the clinical variables or each genomic aberration alone.ConclusionsOur integrative gene signature model shows a significantly improved forecast performance with prognostic and predictive information, and thereby can be served as a biomarker to stratify NB patients for prognosis evaluation and surveillance programs.

Neuronal migration genes and a familial translocation t (3;17): candidate genes implicated in the phenotype

BackgroundWhile Miller-Dieker syndrome critical region deletions are well known delineated anomalies, submicroscopic duplications in this region have recently emerged as a new distinctive syndrome. So far, only few cases have been described overlapping 17p13.3 duplications.MethodsIn this study, we report on clinical and cytogenetic characterization of two new cases involving 17p13.3 and 3p26 chromosomal regions in two sisters with familial history of lissencephaly. Fluorescent In Situ Hybridization and array Comparative Genomic Hybridization were performed.ResultsA deletion including the critical region of the Miller-Dieker syndrome of at least 2,9 Mb and a duplication of at least 3,6 Mb on the short arm of chromosome 3 were highlighted in one case. The opposite rearrangements, 17p13.3 duplication and 3p deletion, were observed in the second case. This double chromosomal aberration is the result of an adjacent 1:1 meiotic segregation of a maternal reciprocal translocation t(3,17)(p26.2;p13.3).Conclusions17p13.3 and 3p26 deletions have a clear range of phenotypic features while duplications still have an uncertain clinical significance. However, we could suggest that regardless of the type of the rearrangement, the gene dosage and interactions of CNTN4, CNTN6 and CHL1 in the 3p26 and PAFAH1B1, YWHAE in 17p13.3 could result in different clinical spectrums.

Genomic arrays identify high-risk chronic lymphocytic leukemia with genomic complexity: a multi-center study.

Complex karyotype identified by chromosome-banding analysis has been shown to have prognostic value in chronic lymphocytic leukemia (CLL). Genomic arrays offer high-resolution genomewide detection of copy-number alterations (CNA) and could therefore be well equipped to detect the presence of a complex karyotype. Current knowledge on genomic arrays in CLL is based on outcomes of single-center studies, in which different cutoffs for CNA calling were used. To further determine the clinical utility of genomic arrays for CNA assessment in CLL diagnostics, we retrospectively analyzed 2,293 arrays from 13 diagnostic laboratories according to established standards. CNA were found outside regions captured by CLL fluorescence in situ hybridization probes in 34% of patients, and several of them, including gains of 8q, deletions of 9p and 18p (P<0.01), were linked to poor outcome after correction for multiple testing. Patients (n=972) could be divided into three distinct prognostic subgroups based on the number of CNA. In multivariable analysis only high genomic complexity, defined as ≥5 CNA, emerged as an independent adverse prognosticator for time to first treatment (hazard ratio: 2.15; 95% confidence interval: 1.36-3.41; P=0.001) and overall survival (hazard ratio: 2.54, 95% confidence interval: 1.54-4.17; P<0.001; n=528). Lowering the size cutoff to 1 Mb in 647 patients did not significantly improve risk assessment. Genomic arrays detected more chromosomal abnormalities and, in terms of risk stratification, performed at least as well as simultaneous chromosome banding analysis as carried out in 122 patients. Our findings indicate that genomic array is an accurate tool for CLL risk stratification.

Cardiomyopathy due to PRDM16 mutation: First description of a fetal presentation, with possible modifier genes.

PRDM16 (positive regulatory domain 16) is localized in the critical region for cardiomyopathy in patients with deletions of chromosome 1p36, as defined by Gajecka et al., American Journal of Medical Genetics, 2010, 152A, 3074-3083, and encodes a zinc finger transcription factor. We present the first fetal case of left ventricular non-compaction (LVNC) with a PRDM16 variant. The third-trimester obstetric ultrasound revealed a hydropic fetus with hydramnios and expanded hypokinetic heart. After termination of pregnancy, foetopathology showed a eutrophic fetus with isolated cardiomegaly. Endocardial fibroelastosis was associated with non-compaction of the myocardium of the left ventricle. Exome sequencing (ES) identified a de novo unreported p.(Gln353*) heterozygous nonsense variant in PRDM16. ES also identified two rare variants of unknown significance, according to the American College of Medical Genetics and Genomics guidelines, in the titin gene (TTN): a de novo missense p.(Lys14773Asn) variant and a c.33043+5A>G variant inherited from the mother. Along with the PRDM16 de novo probably pathogenic variant, TTN VOUS variants could possibly contribute to the severity and early onset of the cardiac phenotype. Because of the genetic heterogeneity of cardiomyopathies, large panels or even ES could be considered as the main approaches for the molecular diagnosis, particularly in fetal presentations, where multiple hits seem to be common.

Prevalence and clinical significance of VHL mutations and 3p25 deletions in renal tumor subtypes.

Purpose: To evaluate prevalence and clinical impact of VHL mutations and deletions (3p), a cohort of consecutive kidney tumors was analyzed by DNA sequencing and fluorescence in-situ hybridization (FISH).Patients and Methods: The study includes 1,805 patients with renal tumors who were surgically treated at the Department of Urology at the University Medical Center Hamburg-Eppendorf between 1994 and 2015. The cohort included 1,176 clear cell, 270 papillary, 101 chromophobe, and 28 clear cell (tubulo) papillary cancers, as well as 149 oncocytomas and 81 less common subtypes.Results: Among 431 successfully analyzed tumors, VHL mutations were found in 59.3% of clear cell, 5.2% of papillary, 3.1% of chromophobe carcinomas and in 7.3% of oncocytomas as well as in the rare kidney tumor types (25%–60%). FISH analysis was successful in 1,403 cases. 3p25 deletion was found in 57.2% of clear cell, 17.6% of papillary, 17.7% of chromophobe carcinomas and in 11.9% of oncocytomas as well as in the rare kidney tumor types (16.7%–50%). No statistically significant associations between VHL mutation/deletion and tumor grade, stage, and clinical outcome was found. Only in the subgroup of papillary cancers, 3p deletion was significantly associated with lymph node and distant metastasis as well as with poor patient outcome (p < 0.05 each).Conclusions: The presence of a VHL mutation in virtually all renal tumor subtypes suggests that VHL analysis cannot be used to distinguish between renal tumor subtypes. Consequently, anti-VHL treatment strategies should not be limited to patients with clear cell cancer.

Large 1p36 Deletions Affecting Arid1a Locus Facilitate Mycn-Driven Oncogenesis in Neuroblastoma

SUMMARYLoss of heterozygosity (LOH) at 1p36 occurs in multiple cancers, including neuroblastoma (NBL). MYCN amplification and 1p36 deletions tightly correlate with markers of tumor aggressiveness in NBL. Although distal 1p36 losses associate with single-copy MYCN tumors, larger deletions correlate with MYCN amplification, indicating two tumor suppressor regions in 1p36, only one of which facilitates MYCN oncogenesis. To better define this region, we genome-edited the syntenic 1p36 locus in primary mouse neural crest cells (NCCs), a putative NBL cell of origin. In in vitro cell transformation assays, we show that Chd5 loss confers most of the MYCN-independent tumor suppressor effects of 1p36 LOH. In contrast, MYCN-driven tumorigenesis selects for NCCs with Arid1a deletions from a pool of NCCs with randomly sized 1p36 deletions, establishing Arid1a as the MYCN-associated tumor suppressor. Our findings reveal that Arid1a loss collaborates with oncogenic MYCN and better define the tumor suppressor functions of 1p36 LOH in NBL.

CURRENT UNDERSTANDING OF THE MOLECULAR MECHANISMS IN ONCOGENESIS OF GASTROINTESTINAL STROMAL TUMORS

The association of genetic driver changes in gastrointestinal stromal tumors (GIST) with clinical implications is the most studied aspect in all solid tumors. Genotyping of particular exons c-KIT and PDGFRA included in the standard practice of diagnosis and treatment of GIST. The review analyzes the current understanding of the molecular-genetic mechanisms and markers that underlie the GIST profiling. Of particular interest are wild-type tumors of c-KIT and PDGFRA, in which activating mutations of the RAS, BRAF and EGFR oncogenes are found, associated with the early stages of disease progression. The data of studies of genetic and epigenetic changes in GIST, which revealed the prognostic value of inactivation of CDKN2A and p53, deletions of 22q, 1p and 15q, CpG hypermethylation are presented. New factors that determine a high risk of progression of GISTs are described: inactivation of dystrophin, DNA hypomethylation, increased expression of miRNAs and HOTAIR. The progress achieved in understanding the molecular mechanisms of GISTs give the opportunity of developing and effectively applying new therapeutic approaches, expanding the range of molecular genetic markers that determine patient surveillance.

Diagnostic and clinical utility of whole genome sequencing in a cohort of undiagnosed Chinese families with rare diseases

Rare diseases are usually chronically debilitating or even life-threatening with diagnostic and therapeutic challenges in current clinical practice. It has been estimated that 80% of rare diseases are genetic in origin, and thus genome sequencing-based diagnosis offers a promising alternative for rare-disease management. In this study, 79 individuals from 16 independent families were performed for whole-genome sequencing (WGS) in an effort to identify the causative mutations for 16 distinct rare diseases that are largely clinically intractable. Comprehensive analysis of variations, including simple nucleotide variants (SNVs), copy-number variations (CNVs), and structural variations (SVs), was implemented using the WGS data. A flexible analysis pipeline that allowed a certain degree of misclassification of disease status was developed to facilitate the identification of causative variants. As a result, disease-causing variants were identified in 10 of the 16 investigated diseases, yielding a diagnostic rate of 62.5%. Additionally, new potentially pathogenic variants were discovered for two disorders, including IGF2/INS-IGF2 in mitochondrial disease and FBN3 in Klippel–Trenaunay–Weber syndrome. Our WGS analysis not only detected a CNV associated with 3p deletion syndrome but also captured a simple sequence repeat (SSR) variation associated with Machado–Joseph disease. To our knowledge, this is the first time the clinical WGS analysis of short-read sequences has been used successfully to identify a causative SSR variation that perfectly segregates with a repeat expansion disorder. After the WGS analysis, we confirmed the initial diagnosis for three of 10 established disorders and modified or corrected the initial diagnosis for the remaining seven disorders. In summary, clinical WGS is a powerful tool for the diagnosis of rare diseases, and its diagnostic clarity at molecular levels offers important benefits for the participating families.

8p deletions in renal cell carcinoma are associated with unfavorable tumor features and poor overall survival

Background and methods8p deletions are common in renal cell carcinoma. To study their prognostic impact and association with kidney cancer phenotype, a tissue microarray with 1,809 cancers was analyzed by fluorescence in situ hybridization for 8p21 copy numbers. ResultsOne thousand four hundred and seventy four interpretable tumors showed substantial differences between renal cancer subtypes. That 8p deletion was only seen in 1 (0.5%) of 216 papillary carcinomas underscores the biologic uniqueness of papillary kidney cancer, which is also defined by a highly distinct morphology. 8p deletions were found in 13.2% of 976 clear cell carcinomas, 7.8% of 77 chromophobe carcinomas, 0.8% of 119 oncocytomas, but also in several rare tumor entities including 1 of 4 collecting duct cancers, 1 of 3 multilocular cystic clear cell renal cell neoplasm of low malignancy, 2 of 10 Xp11.2 translocation cancers, 3 of 18 not otherwise specified carcinomas, and 1 analyzed medullary carcinoma. In clear cell carcinomas, 8p deletions were significantly associated with higher International Society of Urologic Pathologists (ISUP) grading (P = 0.0014), Fuhrman (P = 0.0003) and Thoenes grade (P = 0.0033), advanced tumor stage (P = 0.0002), large tumor diameter (P = 0.0019), distant metastases (P = 0.0183), overall survival (P = 0.0394), and recurrence free survival (P < 0.0001). In multivariate analysis, the prognostic role of 8p deletions was not independent of established clinic-pathological parameters. In conclusion, 8p deletions are strongly linked to tumor aggressiveness in clear cell kidney cancer. ConclusionsBecause 8p deletions are easy to measure by fluorescence in situ hybridization, 8p deletion assessment, most likely in combination with other parameters, may have a role in future prognosis assessment in clear cell kidney cancer.

Comprehensive Analysis of 22 Cases with Blastic Plasmacytoid Dendritic Cell Neoplasm Reveals Mutations in DNA Repair Genes and Two Distinct Subgroups Defined By Differential Gene Expression with Prognostic Impact

Background: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with a poor prognosis. The majority of patients with BPDCN show a complex karyotype. Recurrently mutated genes mainly include epigenetic modifiers and splicing factor genes, however a number of other mutations, many characteristic for myeloid disorders were also detected in BPDCN. Gene expression (GE) profiling revealed an aberrant activation of the NFκB pathway and high expression of BCL2. More recently, rearrangements in MYC were also reported and are associated with an even more aggressive course. However, the exact pathogenesis of BPDCN is still unclear. Aim: Comprehensive analysis of molecular mutations, structural variations and GE profile in 22 cases with BPDCN by whole genome sequencing (WGS) and whole transcriptome sequencing (WTS). Methods: WGS and WTS was performed for 22 BPDCN patients. For WGS, 151bp paired-end reads were generated on NovaSeq 6000 machines (Illumina, San Diego, CA). A mixture genomic DNA from multiple anonymous donors was used as normal controls. All reported p-values are two-sided and were considered significant at p&lt;0.05. For GE analysis, estimated gene counts were normalized and the resulting log2 counts per million were used as a proxy of gene expression in each sample. Results: Median age of the cohort was 74 years (range 16 - 89 years), the majority of patients were male (20/22). After stringent filtering, 112 genes were found recurrently mutated in 22 BPDCN patients. The most frequently mutated genes were epigenetic or splicing factor genes: TET2 (23 mutations (mut) in 15/22 cases, 68%), followed by ASXL1 (7 mut in 7/22 cases, 32%), SRSF2 (7 mut in 7/22 cases, 32%) and ASXL2 (3 mut in 3 3/22 cases, 14%). Moreover, in almost half of the cases (10/22, 45%) a mutation in at least one gene involved in DNA repair (according to Wood et al., Science 2001) was detected: ATM (4 mut in 3 cases), POLH (3 mut in 3 cases), TP53 (2 mut in 1 case), POLE (2 mut in 1 case), REV3L, WRN, MSH6, RAD51C (1 case each). Regarding structural aberrations, deletions of 5q (6/22 cases, 27%), 12p (7/22, 32%), 13q (9/22, 41%), 15q (6/22, 27%) and monosomy 9 (8/22, 36%) were frequently observed. Additionally, we detected gains of 1q and 7q in 4/22 (18%) and 3/22 (14%) cases, respectively. A deletion of TP53 (17p13) was observed in 2/22 (9%) cases. In 4/22 cases (18%) rearrangements involving MYC were observed, the translocation partners were localized on 6p21 (2 cases), 3p24 and 13q14 (1 case, each), respectively. Unsupervised clustering of the whole transcriptional profiles revealed a segregation of the cohort into two distinct groups (see Figure). Interestingly, one group was characterized by a significantly higher expression of the neutrophil-specific receptor CD177 (HNA2A, NB1, PRV1) and CD11b, indicating the presence of an activated subset of neutrophils. This was supported by the pathway enrichment analysis of the differentially expressed genes between both groups, which revealed activation of immune response as a significantly overrepresented biological process. The bimodal expression pattern of CD177 has often been linked to the presence of various SNPs such as A134T, G156A and G1333A (Moritz et al. 2010), however, analysis of the WGS data did not show such a correlation in our cohort. The CD177 gene promotor contains binding sites for the transcription factor CEBPA, which was significantly up-regulated in group 1 and might contribute to the increased expression of CD177. The expression of CD177 has also been linked to overall survival (OS) (Costa et al. 2017) and, interestingly, patients of group 1 showed a longer OS than patients of group 2 (5.9. vs. 3.6 months, p=0.012). Conclusions: (1) Our results give further insight into the complex pattern of genetic aberrations in patients with BPDCN: beside the well-described mutations in epigenetic modifiers and splicing factor genes, a large number of mutations in DNA repair genes (e.g. ATM, POLH, TP53, POLE) were detected. (2) In 18% of our cases, rearrangements involving MYC were detected. (3) GE analysis revealed two different subgroups of BPDCN, differentiated by activation of immune response genes and by the two surface markers CD11b and CD177 with an implication on OS. CD177 is well characterized as an immunotarget and recent studies suggest that CD177-mediated nanoparticle targeting might improve cancer immunotherapy (Chu et al. 2016, Miettinen et al. 2018). Disclosures Stengel: MLL Munich Leukemia Laboratory: Employment. Walter:MLL Munich Leukemia Laboratory: Employment. Baer:MLL Munich Leukemia Laboratory: Employment. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Whole Exome Sequencing Reveals Multiple Driver Events in Chronic Lymphocytic Leukemia Patients with Acquired Ibrutinib Resistance

Disease progression in chronic lymphocytic leukemia (CLL) patients receiving single-agent ibrutinib has been associated with either histological transformation or acquired mutations in BTK and PLCG2 genes which are found in up to 85% of patients with progressive CLL (PD-CLL), less commonly in patients with histologic transformation. Variant allele frequencies of these mutations are highly variable and in some patients remain low and thus cannot fully explain the emergence of drug-resistant clones. Cooperation between mutant and "wild-type" clones has been proposed to explain expansion of clones that have no BTK or PLCG2 mutation. Alternatively, additional drivers have been suggested, including 8p deletion. Here we performed a comprehensive analysis of resistant samples' clonal composition using droplet digital polymerase chain reaction (ddPCR) and whole exome sequencing across multiple time points and compartments to reveal additional hits responsible for drug resistance. Eighty-four CLL patients have been enrolled to a phase II study for ibrutinib monotherapy. Eligible patients had either TP53 aberration or age ≥65 years regardless of prior treatment status. All patients received single-agent ibrutinib 420 mg once daily until disease progression or intolerable side effects occurred. At a median follow-up of 5.5 years, 23 (27.4%) patients developed progressive disease (PD) including 17 patients with PD-CLL, five with Richter's transformation and one with prolymphocytic leukemia. Majority of PD-CLL patients had TP53 aberration (88.2%) and relapsed or refractory CLL (58.8%). The median time-to-progression was 38.8 months for all PD patients and was shorter for those with histologic transformations compared to those with PD-CLL (7.0 vs 44.2 months). We tested for BTK/PLCG2 mutations in 17 PD-CLL patients using archival samples collected at baseline, during response to ibrutinib and at progression using variant-specific ddPCR assays. Fifteen PD-CLL patients (88%) had detectable BTK and/or PLCG2 variants at the time of progression. Notably, only 5 PD-CLL patients (29.4%) demonstrated a strong BTK/PLCG2-driven resistance with cumulative clonal fraction (cCF) above 50% at PD and a significant tumor burden in the peripheral blood (PB). Seven patients (41.2%) demonstrated partial BTK/PLCG2-associated resistance (cCF ranging 4-40%) with additional sub-clonal variants (TP53, NFKBIE, SF3B1, BIRC3, KRAS) and chromosomal aberrations (del8p, del6q, amp2p) as putative drivers in concurrently evolving subclones at PD. Finally, 29.4% of patients had very low (&lt;4%, 3 patients) or undetectable (2 patients) frequencies of BTK/PLCG2 variants but often carried multiple chromosomal aberrations (del17p, del8p, del3p, del2p, del13q) and known CLL driver mutations (NOTCH1, SF3B1) in the resistant clone(s). In all PD-CLL patients, the resistant clones were detected in at least one of the 3 compartments: PB, lymph node (LN) or bone marrow (BM). Expanding clones were present in all 3 sites in three patients (18%), in PB and either LN or BM in 10 (59%) patients, and in LN and/or BM but not in PB in 4 patients (23%). In summary, BTK/PLCG2 mutations are present in most patients progressing on ibrutinib but in many cases these mutations cannot completely account for drug resistance. Exome sequencing followed by clonal decomposition analysis revealed additional genetic alterations in ibrutinib-resistant clones including acquisition of multiple copy number alterations and/or additional known CLL driver mutations. In most patients resistant clones are equally detected in blood and tissue sites. Disclosures Wiestner: Acerta: Research Funding; Merck: Research Funding; Nurix: Research Funding; Pharmayclics: Research Funding.

Relevance of arm somatic copy number alterations for oncologic outcomes and tumor immune microenvironment in clear cell renal cell carcinoma.

Prognostic value of arm somatic copy number alterations (SCNAs) in clear cell renal cell carcinoma (ccRCC) have not been systematically evaluated in a large cohort. Its association with tumor microenvironment remained unknown. We retrospectively correlated arm SCNAs with OS and recurrence free survival (RFS) in a cohort of 524 ccRCC patients. The prognostic landscape of arm SCNA was depicted by bubble heatmap. Associations between arm SCNAs and tumor microenvironment were evaluated by CIBERSORT and Gene Set Enrichment Analysis (GSEA). We found that amplifications of 1p, 3p and loss of 4p, 4q, 5p, 5q, 11p, 11q, 11q, 13q, 19p were independent adverse risk factor for OS, while amplification of 1q and deletions of 4p, 4q, 9p, 9q associated with worse RFS. Loss of 4q were independent adverse risk factor for OS (P=0.012, HR =1.614) and RFS (P=0.001, HR =2.005). It could identify a subset of early stage ccRCC patients with high risk of death and recurrence. CXCL9, CXCL10, CXCL11 mRNA level and CD8+ T cell infiltration were downregulated in ccRCC with 4q deletion. Patients with high arm SCNA level had shorter OS (P=0.005) and RFS (P=0.001). Markers, immune cells and pathways referring to immune suppression were elevated in tumors with high arm SCNA level. In conclusion, loss of 4q was an independent adverse risk factor for OS and RFS in ccRCC patients and contributed to cytotoxic cell exclusion via downregulation of CXCL9, CXCL10 and CXCL11. Patients with higher arm SCNAs had worse survival and a more immunosuppressive tumor microenvironment.