Loss Of Heterozygosity Patterns Research Articles

Genome-wide loss of heterozygosity predicts aggressive, treatment-refractory behavior in pituitary neuroendocrine tumors

Pituitary neuroendocrine tumors (PitNETs) exhibiting aggressive, treatment-refractory behavior are the rare subset that progress after surgery, conventional medical therapies, and an initial course of radiation and are characterized by unrelenting growth and/or metastatic dissemination. Two groups of patients with PitNETs were sequenced: a prospective group of patients (n = 66) who consented to sequencing prior to surgery and a retrospective group (n = 26) comprised of aggressive/higher risk PitNETs. A higher mutational burden and fraction of loss of heterozygosity (LOH) was found in the aggressive, treatment-refractory PitNETs compared to the benign tumors (p = 1.3 × 10−10 and p = 8.5 × 10−9, respectively). Within the corticotroph lineage, a characteristic pattern of recurrent chromosomal LOH in 12 specific chromosomes was associated with treatment-refractoriness (occurring in 11 of 14 treatment-refractory versus 1 of 14 benign corticotroph PitNETs, p = 1.7 × 10−4). Across the cohort, a higher fraction of LOH was identified in tumors with TP53 mutations (p = 3.3 × 10−8). A machine learning approach identified loss of heterozygosity as the most predictive variable for aggressive, treatment-refractory behavior, outperforming the most common gene-level alteration, TP53, with an accuracy of 0.88 (95% CI: 0.70–0.96). Aggressive, treatment-refractory PitNETs are characterized by significant aneuploidy due to widespread chromosomal LOH, most prominently in the corticotroph tumors. This LOH predicts treatment-refractoriness with high accuracy and represents a novel biomarker for this poorly defined PitNET category.

Evolution of loss of heterozygosity patterns in hybrid genomes of Candida yeast pathogens

BackgroundHybrids are chimeric organisms with highly plastic heterozygous genomes that may confer unique traits enabling the adaptation to new environments. However, most evolutionary theory frameworks predict that the high levels of genetic heterozygosity present in hybrids from divergent parents are likely to result in numerous deleterious epistatic interactions. Under this scenario, selection is expected to favor recombination events resulting in loss of heterozygosity (LOH) affecting genes involved in such negative interactions. Nevertheless, it is so far unknown whether this phenomenon actually drives genomic evolution in natural populations of hybrids. To determine the balance between selection and drift in the evolution of LOH patterns in natural yeast hybrids, we analyzed the genomic sequences from fifty-five hybrid strains of the pathogenic yeasts Candida orthopsilosis and Candida metapsilosis, which derived from at least six distinct natural hybridization events.ResultsWe found that, although LOH patterns in independent hybrid clades share some level of convergence that would not be expected from random occurrence, there is an apparent lack of strong functional selection. Moreover, while mitosis is associated with a limited number of inter-homeologous chromosome recombinations in these genomes, induced DNA breaks seem to increase the LOH rate. We also found that LOH does not accumulate linearly with time in these hybrids. Furthermore, some C. orthopsilosis hybrids present LOH patterns compatible with footprints of meiotic recombination. These meiotic-like patterns are at odds with a lack of evidence of sexual recombination and with our inability to experimentally induce sporulation in these hybrids.ConclusionsOur results suggest that genetic drift is the prevailing force shaping LOH patterns in these hybrid genomes. Moreover, the observed LOH patterns suggest that these are likely not the result of continuous accumulation of sporadic events—as expected by mitotic repair of rare chromosomal breaks—but rather of acute episodes involving many LOH events in a short period of time.

Loss of Heterozygosity in the Circulating Tumor DNA and CD138+ Bone Marrow Cells in Multiple Myeloma.

Multiple myeloma (MM) is characterized by heterogeneity of tumor cells. The study of tumor cells from blood, bone marrow, plasmacytoma, etc., allows us to identify similarities and differences in tumor lesions of various anatomical localizations. The aim of this study was to compare the loss of heterozygosity (LOH) by tumor cells by assessing STR profiles of different MM lesions. We examined paired samples of plasma circulating tumor DNA (ctDNA) and CD138+ bone marrow cells in MM patients. For patients with plasmacytomas (66% of 38 patients included), the STR profile of plasmacytomas was also studied when biopsy samples were available. Diverse patterns of LOH were found in lesions of different localization for most patients. LOH in plasma ctDNA, bone marrow, and plasmacytoma samples was found for 55%, 71%, and 100% of patients, respectively. One could expect a greater variety of STR profiles in aberrant loci for patients with plasmacytomas. This hypothesis was not confirmed-no difference in the frequency of LOH in MM patients with or without plasmacytomas was found. This indicates the genetic diversity of tumor clones in MM, regardless of the presence of extramedullar lesions. Therefore, we conclude that risk stratification based on molecular tests performed solely on bone marrow samples may not be sufficient for all MM patients, including those without plasmacytomas. Due to genetic heterogeneity of MM tumor cells from various lesions, the high diagnostic value of liquid biopsy approaches becomes obvious.

Value of the loss of heterozygosity to BRCA1 variant classification

At least 10% of the BRCA1/2 tests identify variants of uncertain significance (VUS) while the distinction between pathogenic variants (PV) and benign variants (BV) remains particularly challenging. As a typical tumor suppressor gene, the inactivation of the second wild-type (WT) BRCA1 allele is expected to trigger cancer initiation. Loss of heterozygosity (LOH) of the WT allele is the most frequent mechanism for the BRCA1 biallelic inactivation. To evaluate if LOH can be an effective predictor of BRCA1 variant pathogenicity, we carried out LOH analysis on DNA extracted from 90 breast and seven ovary tumors diagnosed in 27 benign and 55 pathogenic variant carriers. Further analyses were conducted in tumors with PVs yet without loss of the WT allele: BRCA1 promoter hypermethylation, next-generation sequencing (NGS) of BRCA1/2, and BRCAness score. Ninety-seven tumor samples were analyzed from 26 different BRCA1 variants. A relatively stable pattern of LOH (65.4%) of WT allele for PV tumors was observed, while the allelic balance (63%) or loss of variant allele (15%) was generally seen for carriers of BV. LOH data is a useful complementary argument for BRCA1 variant classification.

A Turner syndrome case associated with dic(Y;22)

BackgroundConstitutional telomeric associations are very rare events and the mechanism underlying their development is not well understood.Case presentationWe here describe a female case of Turner syndrome with a 45,X,add(22)(p11.2)[25]/45,X[5]. We reconfirmed this karyotype by FISH analysis as 45,X,dic(Y;22)(p11.3;p11.2)[28]/45,X[2].ish dic(Y;22)(SRY+,DYZ1+). A possible mechanism underlying this mosaicism was a loss of dic(Y;22) followed by a monosomy rescue of chromosome 22. However, SNP microarray analysis revealed no loss of heterozygosity (LOH) in chromosome 22, although a mosaic pattern of LOH was clearly detectable at the pseudoautosomal regions of the sex chromosomes.ConclusionsOur results suggest that the separation of the dicentric chromosome at the junction resulted in a loss of chromosome Y without a loss of chromosome 22, leading to this patient’s unique mosaicism. Although telomere signals were not detected by FISH at the junction, it is likely that the original dic(Y;22) chromosome was generated by unstable telomeric associations. We propose a novel “pulled apart” mechanism as the process underlying this mosaicism.

Loss of Heterozygosity and Base Mutation Rates Vary Among Saccharomyces cerevisiae Hybrid Strains.

A growing body of evidence suggests that mutation rates exhibit intra-species specific variation. We estimated genome-wide loss of heterozygosity (LOH), gross chromosomal changes, and single nucleotide mutation rates to determine intra-species specific differences in hybrid and homozygous strains of Saccharomyces cerevisiae. The mutation accumulation lines of the S. cerevisiae hybrid backgrounds - S288c/YJM789 (S/Y) and S288c/RM11-1a (S/R) were analyzed along with the homozygous diploids RM11, S288c, and YJM145. LOH was extensive in both S/Y and S/R hybrid backgrounds. The S/Y background also showed longer LOH tracts, gross chromosomal changes, and aneuploidy. Short copy number aberrations were observed in the S/R background. LOH data from the S/Y and S/R hybrids were used to construct a LOH map for S288c to identify hotspots. Further, we observe up to a sixfold difference in single nucleotide mutation rates among the S. cerevisiae S/Y and S/R genetic backgrounds. Our results demonstrate LOH is common during mitotic divisions in S. cerevisiae hybrids and also highlight genome-wide differences in LOH patterns and rates of single nucleotide mutations between commonly used S. cerevisiae hybrid genetic backgrounds.

Abstract 2702: Analysis of low-pass sequencing data reveals extensive loss-of-heterozygosity in circulating multiple myeloma cells

Abstract Background: Clonal evolution and heterogeneity are among the factors that make treatment of Multiple Myeloma (MM) challenging, and disease monitoring requires invasive bone marrow biopsies. Tumor heterogeneity has previously been demonstrated at copy-number level, showing patterns of recurring Copy-Number Alterations (CNA). Conversely, Loss-of-Heterozygosity (LoH) profiling has been investigated less extensively. Presence of genomic patterns of LoH has been associated with Homologous Recombination Deficiency (HRD) in MM, suggesting a role for therapy with PARP inhibitors. Here we report the genome-wide LoH profiling in single-CMMCs isolated from enriched peripheral blood of four different MM patients using a non-invasive approach that combines CellSearch® and DEPArray™ technology. Methods: CMMCs were obtained from peripheral blood of four MM patients using CellSearch for enrichment and DEPArray NxT for isolation. CMMCs enrichment was obtained using a custom kit with anti-CD138 or anti-CD138/CD38 antibody-conjugated ferrofluids for positive enrichment and CD38-PE, CD19/CD45-APC immunofluorescent staining for detection. After single cell isolation, Ampli1™ Whole Genome Amplification (WGA) kit was used to amplify single-cell genomic DNA. Whole genome sequencing libraries were prepared from WGA products using Ampli1™ LowPass kit and low-pass sequencing was performed on HiSeq 2500 Illumina® platform. Genome-wide single-cell Low-Pass Copy Number Alteration (LPCNA) analysis was performed using the cloud-based bioinformatic suite MSBiosuite. Single-cell genome-wide LoH profiles were obtained by a custom algorithm based on the ratio between mono- and bi-allelic loci in non-overlapping segments of uniform copy-number. Results: Out of 315 cells analyzed from the four MM patients, 244 (77%) showed LoH events. Extensive LoH regions were detected in all patients, with 231 cells showing copy-neutral LoH events and 121 showing LoH events in copy-gain regions. Globally, 460 copy-neutral LoHs, and 292 LoHs in copy-gain regions were detected. Two highly conserved copy-neutral events (9p; 16q) were detected in one of the patients analyzed, suggesting they are early events. Interestingly, the first of the 2 events includes CDKN2A, a tumor suppressor which has been implicated in predisposition to MM. Notably, in a second patient, chromosome 11 is associated both to a copy-neutral LoH and to an LoH event in a copy-gain segment including the CCND1 gene, whose amplification in MM has been associated with multidrug resistance expression. Conclusions: Here we present a non-invasive workflow for the molecular characterization of single CMMCs isolated from peripheral blood. Specifically, we reported the presence of chromosomal or sub-chromosomal LoH events in all MM patients, suggesting a pervasive phenomenon in MM which deserves to be further explored as potential therapy target. Citation Format: Claudio Forcato, Alberto Ferrarini, Genny Buson, Paola Tononi, Marianna Garonzi, Valentina del Monaco, Andrea Raspadori, Steven Gross, Francesca Fontana, Gianni Medoro, Mark Connelly, Nicolò Manaresi. Analysis of low-pass sequencing data reveals extensive loss-of-heterozygosity in circulating multiple myeloma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2702.

Patterns of chromosome 18 loss of heterozygosity in multifocal ileal neuroendocrine tumors.

Ileal neuroendocrine tumors (NETs) represent the most common neoplasm of the small intestine. Although up to 50% of patients with ileal NETs are diagnosed with multifocal disease, the mechanisms by which multifocal ileal NETs arise are not yet understood. In this study, we analyzed genome‐wide sequencing data to examine patterns of copy number variation in 40 synchronous primary ileal NETs derived from three patients. Chromosome (chr) 18 loss of heterozygosity (LOH) was the most frequent copy number alteration identified; however, not all primary tumors from the same patient had evidence of this LOH. Our data revealed three distinct patterns of chr18 allelic loss, indicating that primary tumors from the same patient can present different LOH patterns including retention of either parental allele. In conclusion, our results are consistent with the model that multifocal ileal NETs originate independently. In addition, they suggest that there is no specific germline allele on chr18 that is the target of somatic LOH.

Clonal relationship of synchronous head and neck cancer and esophageal cancer assessed by single nucleotide polymorphism-based loss of heterozygosity analysis

BackgroundThe prognoses of head and neck squamous cell carcinoma (HNSCC) and esophageal squamous cell carcinoma (ESCC) are poor, especially when both tumors occur at the same time. We examined the clonal relatedness of HNSCCs with synchronous ESCCs to confirm whether the second tumors were metastasis or separate second primary malignancies (SPMs) using loss of heterozygosity (LOH) analysis.MethodsTwenty-one pairs of formalin-fixed paraffin-embedded tissue from HNSCC patients with synchronous esophageal cancer were analyzed by single nucleotide polymorphism (SNP) array using the Illumina HumanCytoSNP FFPE-12 BeadChip (San Diego, CA), which contains approximately 300,000 probes. LOH was identified using Nexus Copy Number software (El Segundo, CA).ResultsComparing the LOH pattern between HNSCC and paired ESCC, we found that 20 out of 21 paired tissues had a high number of discordant LOHs (LOH identified solely in the primary HNSCC but not in synchronous ESCC at the same genomic location) and a low number of concordant LOHs (LOH at the same genomic location in both HNSCC and ESCC). Only one case fell into the undetermined category. Therefore, these 20 ESCCs were classified as SPMs or second field tumors (SFTs). Moreover, the HNSCC patients with molecularly confirmed esophageal SPM had significantly poorer survival than the other patients.ConclusionsWe propose the use of a genome-wide SNP array as a tool to differentiate metastatic tumors from SPM/SFT. The SNP array offers genome-wide LOH information that earlier microsatellite analysis studies lack. The ability to accurately identify SPM should contribute to a better treatment plan and follow-up care of these patients.

Whole-Genome Sequencing of the Opportunistic Yeast Pathogen Candida inconspicua Uncovers Its Hybrid Origin.

Fungal infections such as those caused by Candida species are increasingly common complications in immunocompromised patients. The list of causative agents of candidiasis is growing and comprises a set of emerging species whose relative global incidence is rare but recurrent. This is the case of Candida inconspicua, which prevalence has increased 10-fold over the last years. To gain novel insights into the emergence of this opportunistic pathogen and its genetic diversity, we performed whole genome sequencing of the type strain (CBS180), and of 10 other clinical isolates. Our results revealed high levels of genetic heterozygosity structured in non-homogeneous patterns, which are indicative of a hybrid genome shaped by events of loss of heterozygosity (LOH). All analyzed strains were hybrids and could be clustered into two distinct clades. We found large variability across strains in terms of ploidy, patterns of LOH, and mitochondrial genome heterogeneity that suggest potential admixture between hybrids. Altogether, our results identify a new hybrid species with virulence potential toward humans and underscore the potential role of hybridization in the emergence of novel pathogenic lineages.

Loss of Heterozygosity and Possible Loss of Allele Amplification in Homozygous Short Tandem Repeats Loci in Two ALL Patients with Central Nervous System and Bone Marrow Relapses

Introduction: Loss of heterozygosity (LOH) was described for many forms of cancer including leukemia. LOH may contribute to oncogenesis through the deletion of tumor suppressor genes due to appropriate allelic loss. LOH in short tandem repeats loci (STR) has been reported for solid tumors and is widely used as malignant cells population marker. It should be noted that little is known yet about possible loss of one of certain homozygous alleles in tumour cells and STR analysis might be a promising approach to investigate this phenomenon. STR analysis is used as a routine test for chimerism monitoring after bone marrow transplantation. It could not also be excluded that recipient's chimerism estimation may be distorted in some cases due to LOH issues.The aim: To investigate possible allele loss in homozygous loci in tumour cells and to assess the contribution of LOH to the error in mixed chimerism estimation.Patients and Methods: This study includes analysis of STR DNA-profiles of two ALL patients after allogeneic stem cells transplantation. Patient 1 was 54 years old female with B-ALL, she underwent allogenic BM transplantation but after it she had four central nervous system (CNS) relapses and three bone marrow relapses. Patient 2 was 23 years old male with preT-ALL, two CNS relapses: first before transplantation and second after it. The DNAs were isolated from bone marrow samples of patients in remission before transplantation, from donors blood samples, from cerebrospinal fluid during neuro relapse and from bone marrow samples. The presence of blast cells in bone marrow samples and cerebrospinal fluid was confirmed morphologically and cytogenetically. STR-profiles were assessed by polymerase chain reaction with COrDIS Plus multiplex kit for amplification of 19 polymorphic STR-markers and amelogenin loci (Gordiz Ltd, Russia). The fragment analysis was performed on ABI3130 Genetic Analyzer. The data processing was accomplished using GeneMapper v.4-0 software.Results: The STR profile analysis for Patient 1 showed complete recipient chimerism in cerebrospinal fluid with LOH in 10 from 15 heterozygous loci (Fig.1a,b) comparative to control sample of DNA (bone marrow before transplantation). The same LOH pattern was detected in archival DNA sample from first spinal relapse. Mixed chimerism in bone marrow samples estimated by STR analysis was equal to blast cell percentage assessed by cytogenetics. Loss of non-informative allele in D16S539 (Fig.1b) didn't distort chimerism estimation. However decreased levels of mixed chimerism were calculated in two homozygous loci (Fig.1a,c). We suspected that this decrease could be caused by the loss of one allele amplification in homozygous locus. Therefore, we proposed the mathematical model f(x), where x - is donor percentage in chimera, f(x) - difference between real recipient percentage (100-x) and calculated for locus with loss of allele amplification ((100-x)/2:((100-x)/2+x))*100% (Fig.1c) to test this hypothesis. The highest difference in chimerism calculation (about 17%) is expected in about 40% of donor and 60% recipient percentage. For Patient 2 the STR analysis detected only one LOH locus in DNA samples from cerebrospinal fluid during CNS relapse before and after BMT. However this patient has eight homozygous STR loci and complete donor chimerism in bone marrow. To find possible “loss of allele amplification” we used the artificial chimera, the mix of Patient 2 and unrelated random healthy donor DNA (Fig.1d). We used control DNA of Patient 2 (bone marrow before BMT) to check chimerism level deviations in loci of interest. The decreased level of mixed chimerism was detected in two homozygous loci from cerebrospinal fluid DNA-sample. The decreased estimate for chimerism correlated with proposed math model. For the same STR loci in control DNA no chimerism deviations were detected in mixed artificial chimera (Fig.1e).Conclusions: The LOH loci pattern might be preserved during long period of disease for certain malignant clone. Mixed chimerism or artificial mixed chimera can be useful in finding of homozygous loci with loss of one allele amplification. We suppose homozygous loci are the preferable subject for investigating LOH mechanisms. Loci with “loss of allele amplification” might be the used as malignant cells population marker.This study was supported by the Russian Foundation for Basic Research (RFBR) grant 18-015-00399a. DisclosuresRisinskaya:Russian Foundation for Basic Research grant 18-015-00399 A: Research Funding. Chabaeva:Russian Foundation for Basic Research grant 18-015-00399 A: Research Funding. Kulikov:Russian Foundation for Basic Research grant 18-015-00399 A: Research Funding.

Recurrent loss of heterozygosity correlates with clinical outcome in pancreatic neuroendocrine cancer

Pancreatic neuroendocrine tumors (pNETs) are uncommon cancers arising from pancreatic islet cells. Here we report the analysis of gene mutation, copy number, and RNA expression of 57 sporadic well-differentiated pNETs. pNET genomes are dominated by aneuploidy, leading to concordant changes in RNA expression at the level of whole chromosomes and chromosome segments. We observed two distinct patterns of somatic pNET aneuploidy that are associated with tumor pathology and patient prognosis. Approximately 26% of the patients in this series had pNETs with genomes characterized by recurrent loss of heterozygosity (LoH) of 10 specific chromosomes, accompanied by bi-allelic MEN1 inactivation and generally poor clinical outcome. Another ~40% of patients had pNETs that lacked this recurrent LoH pattern but had chromosome 11 LoH, bi-allelic MEN1 inactivation, and universally good clinical outcome. The somatic aneuploidy allowed pathogenic germline variants (e.g., ATM) to be expressed unopposed, with RNA expression patterns showing inactivation of downstream tumor suppressor pathways. No prognostic associations were found with tumor morphology, single gene mutation, or expression of RNAs reflecting the activity of immune, differentiation, proliferative or tumor suppressor pathways. In pNETs, single gene mutations appear to be less important than aneuploidy, with MEN1 the only statistically significant recurrently mutated driver gene. In addition, only one pNET in the series had clearly actionable single nucleotide variants (SNVs) (in PTEN and FLCN) confirmed by corroborating RNA expression changes. The two clinically relevant patterns of LoH described here define a novel oncogenic mechanism and a plausible route to genomic precision oncology for this tumor type.

Molecular determination of the clonal relationships between multiple tumors in BRCA1/2-associated breast and/or ovarian cancer patients is clinically relevant

Female BRCA1/2 mutation carriers affected with breast and/or ovarian cancer may develop new tumor deposits over time. It is of utmost importance to know the clonal relationships between multiple tumor localizations, enabling differentiation between multiple primaries or metastatic disease with consequences for therapy and prognosis. We evaluated the value of targeted next generation sequencing in the diagnostic workup of BRCA1/2 mutation carriers with ≥2 tumor localizations and uncertain tumor origins. Forty-two female BRCA1/2 mutation carriers with ≥2 tumor localizations were selected. Patients with inconclusive tumor origin after histopathological revision were ‘cases'; patients with certain tumor origin of ≥3 tumors served as ‘controls'. Tumors of cases and controls were analyzed by targeted next generation sequencing using a panel including CDKN2A, PTEN and TP53, hotspot mutation sites for 27 different genes and 143 single nucleotide polymorphisms for detection of loss of heterozygosity. Based on prevalence of identical or different mutations and/or loss of heterozygosity patterns, tumors were classified as ‘multiple primaries' or ‘one entity'. Conventional histopathology yielded a conclusive result in 38/42 (90%) of patients. Four cases and 10 controls were analyzed by next generation sequencing. In 44 tumor samples, 48 mutations were found; 39 (81%) concerned TP53 mutations. In all 4 cases, the intra-patient clonal relationships between the tumor localizations could be unequivocally identified by molecular analysis. In all controls, molecular outcomes matched the conventional histopathological results. In most BRCA1/2 mutation carriers with multiple tumors routine pathology work-up is sufficient to determine tumor origins and relatedness. In case of inconclusive conventional pathology results, molecular analyses using next generation sequencing can reliably determine clonal relationships between tumors, enabling optimal treatment of individual patients.

Combined hepatocellular and cholangiocarcinoma originating from the same clone: a pathomolecular evidence-based study

BackgroundCombined hepatocellular and cholangiocarcinoma (CHC) is a unique subtype of liver cancer comprising both hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC); however, its cellular origin remains unclear. The purpose of this study was to investigate the clinicopathologic features and the clonal relationship between HCC and ICC in 34 patients with CHC.MethodsThe clinicopathologic features and prognosis of the 34 CHC patients were compared with those of 29 patients with separated HCC and ICC (SHC). Loss of heterozygosity (LOH) at 10 highly polymorphic microsatellite markers was detected in 16 CHC and 10 SHC tissues for determination of the clonal origin of CHC. Expression of hepatocyte markers [hepatocyte paraffin 1 (Hep Par 1) and glypican 3 (GPC3)] and cholangiocyte markers [cytokeratin (CK)7 and 19] in tumor tissues was examined by immuno histochemical analysis.ResultsIn the 16 CHC specimens, the difference in LOH patterns between HCC and ICC was less than 30%, suggesting the same clonal origin of HCC and ICC. Consistent with this finding, immunohistochemical analysis revealed that hepatocyte markers (Hep Par 1 and GPC3) and cholangiocyte markers (CK7 and CK19) were simultaneously expressed in both the HCC and ICC components in 52.9% of CHC specimens, suggesting that the two components shared a similar phenotype with hepatic progenitor cells (HPCs). On the contrary, in all 10 SHC cases, the difference in LOH patterns between the HCC and ICC components was greater than 30%, suggesting different clonal origins of HCC and ICC. Overall survival and disease-free survival were shorter for patients with CHC than for patients with SHC (P < 0.05).ConclusionsOur results suggest that the HCC and ICC components of CHC may originate from the same clone, having the potential for dual-directional differentiation similar to HPCs. CHC tended to exhibit the biological behaviors of both HCC and ICC, which may enhance the infiltrative capacity of tumor cells, leading to poor clinical outcomes for patients with CHC.

Abstract 3164: Molecular determination of the clonal relationship between multiple tumors in BRCA1/2-associated cancer patients has clinical relevance

Abstract PURPOSE Female BRCA1/2 mutation carriers commonly develop breast cancer and ovarian cancer. It is of utmost importance to know the clonal relationship between multiple tumor localizations, (multiple primaries or metastasized disease), since prognosis and treatment differ between these tumors and their metastases. We evaluated the value of targeted Next Generation Sequencing (NGS) in the diagnostic workup of BRCA1/2 mutation carriers with ≥2 tumor localizations and uncertain tumor origins. METHODS Forty-two female BRCA1/2 mutation carriers with ≥2 tumor locations with tumor material available for pathologic revision were selected. Median age at first cancer diagnosis was 48.0 years (range 30-68). Four patients with inconclusive tumor origin after histological and immunohistochemical analyses were ‘cases’; 10 patients with certain tumor origin of ≥3 tumors served as ‘controls’. Tumors of cases and controls were analyzed by targeted NGS using a panel including CDKN2A, PTEN and TP53, hotspot mutation sites for 27 different genes and 143 single nucleotide polymorphisms for detection of loss of heterozygosity (LOH). Based on prevalence of identical or different mutations and/or LOH patterns, tumors were classified as ‘multiple primaries’ or ‘one entity’. RESULTS In 44 tumors, 48 mutations were found; 39 (81%) concerned TP53 mutations. In all 10 controls and all 4 cases, the intrapatient clonal relationships between the tumors could be unequivocally identified by molecular analysis. In all controls, tumor origins based on molecular outcomes matched the conventional histopathological diagnosis. CONCLUSION In 90% of BRCA1/2 mutation carriers with multiple tumors routine pathology work-up is sufficient to determine tumor origins and relatedness. In case of inconclusive conventional pathology results, molecular analyses using NGS can reliably determine clonal relationships between tumors, enabling optimal treatment of individual patients. Citation Format: Willemina R.R. Geurts-Giele, Victorien M.T. van Verschuer, Carolien H.M. van Deurzen, Paul J. van Diest, Rute M. Pedrosa, J. Margriet Collee, Linetta B. Koppert, Caroline Seynaeve, Winand N.M. Dinjens. Molecular determination of the clonal relationship between multiple tumors in BRCA1/2-associated cancer patients has clinical relevance. [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 3164.

Clonal and genetic relationship between individual components of mucoepidermoid carcinoma: X-chromosome inactivation assay and microsatellite analysis

Mucoepidermoid carcinoma is a common salivary gland malignancy characterized by genetic heterogeneity as well as cellular diversity of its neoplastic components, which include mucinous cells, epidermoid cells and intermediate cells. The clonal and genetic relationship between each component has not been investigated before, and it is unclear whether these three phenotypically distinct components differ genetically. Each component from all 21 cases was precisely microdissected and examined by microsatellite loss of heterozygosity (LOH) analysis with a panel of 5 microsatellite markers: D2S125, D5S417, D6S297, D6S1577, and D11S1311. In addition, X-chromosome inactivation assay was performed in the components from 18 female cases. The number of microdissected components varied from 2 to 3 depending on the quantity of each cell subpopulation. Histopathological observation indicated that these three components shared an inseparable connection. Identical patterns of X-chromosome inactivation were shared among all the components in 9 of the 11 available informative cases. Of these 9 cases, 5 cases showed partially or totally discordant LOH patterns. Microsatellite analyses revealed discordant LOH patterns in 9 cases, 4 of which were corroborated to have identical X-chromosome inactivation patterns. Concordant LOH patterns were observed in all the components in 3 cases. These data suggest that heterologous components in most mucoepidermoid carcinomas are monoclonally originated. Individual components displayed identical and/or distinct LOH, implying that disparate genetic changes were implicated in the process of phenotypic divergence.

Humanized Mouse Model of Myeloma Reveals Clinically Occult Genomic Changes in Primary Tumor Cells

Next generation sequencing of purified plasma cells from myeloma patients has revealed the genomic complexity of tumors and is being utilized for developing personalized approaches to therapy. Evaluation of functional properties of these genetic changes and the growth potential of human tumors / their subclones has been limited by difficulties in reliable engraftment of primary human tumor cells in mice. The growth of human cells in mice is limited in part due to the presence of species non-cross-reactive cytokines/growth factors and innate immune rejection mechanisms. In order to overcome these barriers, we designed MISKI TRG6 mice, wherein human IL6 was additionally knocked in on the backbone of MISKI TRG mice. Both MISTRG and MISKI TRG support enhanced engraftment of human hematoipoietic cells (Rongvaux et al. Nat Biotechnol. 2014) and the addition of IL6 provides an essential MM growth factor. Injection of primary tumor cells from MM patients led to reliable engraftment of primary tumor cells in these mice. In this study, we utilized whole exome sequencing (WES) to compare the genomic changes in paired tumors isolated from (n=3) patients versus those growing in xenografts. In some patients, tumor cells from more than one xenografted mouse were analyzed separately to allow for evaluation of tumors growing in each individual mouse. Tumor cells were sorted by flow cytometry and subjected to DNA isolation followed by whole exome capture and sequencing. Germline and tumor DNA were captured on a Roche NimbleGen Sequence Capture V2.0 human exome array following the manufacturer's protocol, with protocol modifications at the Yale Center for Genome Analysis. Captured libraries were sequenced on the HiSeq 2500 sequencing system. Analysis of sequencing data was performed with the Yale exome-sequencing pipeline, as described (Choi et al. Nat. Genet. 2015). Mean depth of coverage for primary and xenografted samples was comparable. Comparison of loss of heterozygosity (LOH) patterns revealed that the majority of LOH changes in baseline tumors were also observed in xenografts, but the latter also contained additional changes. Profile of somatic copy number alterations (CNA) also revealed that while the xenografts captured the majority of CNA detected in freshly isolated tumor cells, they also exhibited additional genomic changes not detected in the initial tumor. Importantly, this included genomic changes in chromosome 1 typically associated with high-risk MM. Interestingly, the pattern of LOH and CNA were identical in individual mice transplanted with the same tumor cells, indicating that the new patterns of genomic changes observed in xenografts were likely already present at baseline, but clinically occult as in a minor subclone. Analysis of somatic non-synonymous variants (SNVs) revealed that the great majority of SNVs detected in the parent tumor were also identified in the xenografts, which also contained additional SNVs not detected at baseline. This included some targetable SNVs with known oncogenic potential. Together, these data demonstrate the capacity of MISKI TRG6 mice to recapitulate the genomic complexity of primary MM tumor cells and reveal their growth potential. These data provide a novel approach to investigate the genetics of human plasma cell neoplasia in vivo and reveal subclinical genetic lesions that may contribute to future relapse. Humanized models may be essential to fully understand genomic complexity of human tumors at a functional level and to optimize personalized approaches to therapy of human MM. DisclosuresNo relevant conflicts of interest to declare.

Profiling Loss of Heterozygosity Patterns in a Cohort of Favorable Histology Nephroblastoma Egyptian Patients: What is Consistent With the Rest of the World

According to the Fifth National Wilms Tumor Study (NWTS-5), tumor-specific loss of heterozygosity (LOH) for chromosomes 1p and 16q identifies a subset of patients with Wilms tumor (WT) who despite having favorable histology (FH) have a significantly increased risk of relapse and death. We aimed to find out 1p and 16q LOH frequencies in patients with FH-WT as well as its correlation to survival outcome and epidemiologic and clinical characteristics. Data of patients with FH-WT presenting to the National Cancer Institute, Egypt, were retrospectively analyzed. Paraffin blocks were tested for 1p and 16q LOH using polymorphic loci that span the minimal regions of LOH at this area. The study included 100 patients with a median age of 5 years. Thirty-nine patients (39%) showed LOH at 1p (n = 14), 16q (n = 13), or both (n = 12). LOH was most frequently encountered in patients above 10 years (5/5), advanced stages disease (80% of stage V and 50% of stages IV and III each). The 3-year overall survival (OS) and event-free survival (EFS) were significantly lower in patients with double LOH (75% and 50%, respectively), followed by 16q (92% and 54%), in comparison with 1p (93% each) and negative LOH (97% and 100%) cases, respectively (p = 0.001). Combined LOH (1p+16q), followed by 16q LOH alone, was predictive of poorer outcome and was associated with lower OS and EFS in patients with FH-WT. Our results showed a higher-risk disease that would suggest the need for an intensified upfront therapy in this group of patients.

Observations of the genomic landscape beyond 1p19q deletions and EGFR amplification in glioma.

BackgroundWith recent advancements in molecular techniques, the opportunities to gather whole genome information have increased, even in degraded samples such as FFPE tissues. As a result, a broader view of the genomic landscape of solid tumors may be explored. Whole genome copy number and loss of heterozygosity patterns can advance our understanding of mechanisms and complexity of various tumors.ResultsGenome-wide alterations involving copy number changes and loss of heterozygosity were identified in 17 glioma samples with positive FISH results for 1p19q co-deletions (n = 9) or EGFR amplification (n = 8). Gliomas positive for 1p19q co-deletions did not have other frequently recurrent genomic alterations. Additional copy-number alterations were observed in individual cases, and consisted primarily of large-scale changes, including gains or losses of entire chromosomes. The genomic architecture of EGFR amplified gliomas was much more complex, with a high number of gains and losses across the genome. Recurrent alterations in EGFR amplified gliomas were both focal, such as CDKN2A homozygous deletions, and large, such as chromosome 10 loss.ConclusionsMicroarray enabled a broader picture of the genomic alterations occurring in glioma cases. Gliomas with 1p19q co-deletion had a relatively quiet genome, apart from the selected co-deletion. Additional alterations in isolated cases, involved primarily larger aberrations. On the other hand, EGFR amplified cases tended to be more complex and have specific abnormalities associated with the EGFR amplification. Furthermore, 1p19q co-deletions and EGFR amplification associated copy number changes appeared to often be mutually exclusive.

Association between histopathological features of dysplasia in oral leukoplakia and loss of heterozygosity

Oral leukoplakia (OL) dysplasia is graded on the basis of architectural and cytological features, and grade does not correlate well with malignant transformation. Loss of heterozygosity (LOH) profiles have been validated as risk predictors of OL malignant transformation. We aimed to assess whether the histological parameters used to grade dysplasia show different LOH profiles. Areas of epithelial dysplasia of 29 OL samples were microdissected, and LOH was assessed by use of a panel of 11 microsatellite markers located on chromosomes 3, 9, 11, and 17. Dysplasia was graded, and the cytological and architectural parameters were scored. Dysplasia was graded as mild in 18 samples, moderate in nine, and severe in two. The moderate/severe dysplasias and the mild dysplasias did not show different frequencies of allelic loss. Irregular epithelial stratification was associated with LOH at marker D3S1234 (3p14.2). In addition, the presence of drop-shaped rete ridges and premature keratinization in single cells showed associations with LOH at D9S162 (9p22) and P53 (17p13.1), respectively. We provide evidence that architectural and cellular changes in OL have different LOH patterns.