A LINE-1 mediated deletion resulting in germline retinoblastoma predisposition.

Retinoblastoma is an ocular cancer associated with genomic variation in the RB1 gene. In individuals with bilateral retinoblastoma, a germline variant in RB1 is identified in virtually all cases. We describe herein an individual with bilateral retinoblastoma for whom multiple clinical lab assays performed by outside commercial laboratories failed to identify a germline RB1 variant. Paired tumor/normal exome sequencing, long-read whole genome sequencing, and long-read isoform sequencing was performed on a translational research basis ultimately identified a germline likely de novo Long Interspersed Nuclear Element (LINE)-1 mediated deletion resulting in a premature stop of translation of RB1 as the underlying genetic cause of retinoblastoma in this individual. Based on these research findings, the LINE-1 mediated deletion was confirmed via Sanger sequencing in our clinical laboratory, and results were reported in the patient's medical record to allow for appropriate genetic counseling.

Expanding the Clinical Utility of Targeted RNA Sequencing Panels beyond Gene Fusions to Complex, Intragenic Structural Rearrangements.

Gene fusions are a form of structural rearrangement well established as driver events in pediatric and adult cancers. The identification of such events holds clinical significance in the refinement, prognostication, and provision of treatment in cancer. Structural rearrangements also extend beyond fusions to include intragenic rearrangements, such as internal tandem duplications (ITDs) or exon-level deletions. These intragenic events have been increasingly implicated as cancer-promoting events. However, the detection of intragenic rearrangements may be challenging to resolve bioinformatically with short-read sequencing technologies and therefore may not be routinely assessed in panel-based testing. Within an academic clinical laboratory, over three years, a total of 608 disease-involved samples (522 hematologic malignancy, 86 solid tumors) underwent clinical testing using Anchored Multiplex PCR (AMP)-based RNA sequencing. Hematologic malignancies were evaluated using a custom Pan-Heme 154 gene panel, while solid tumors were assessed using a custom Pan-Solid 115 gene panel. Gene fusions, ITDs, and intragenic deletions were assessed for diagnostic, prognostic, or therapeutic significance. When considering gene fusions alone, we report an overall diagnostic yield of 36% (37% hematologic malignancy, 41% solid tumors). When including intragenic structural rearrangements, the overall diagnostic yield increased to 48% (48% hematologic malignancy, 45% solid tumor). We demonstrate the clinical utility of reporting structural rearrangements, including gene fusions and intragenic structural rearrangements, using an AMP-based RNA sequencing panel.

EGFR internal tandem duplications in fusion-negative congenital and neonatal spindle cell tumors.

Next-generation sequencing (NGS) assays can sensitively detect somatic variation, and increasingly can enable the identification of complex structural rearrangements. A subset of infantile spindle cell sarcomas, particularly congenital mesoblastic nephromas with classic or mixed histology, have structural rearrangement in the form of internal tandem duplications (ITD) involving EGFR. We performed prospective analysis to identify EGFR ITD through clinical or research studies, as well as retrospective analysis to quantify the frequency of EGFR ITD in pediatric sarcomas. Within our institution, three tumors with EGFR ITD were prospectively identified, all occurring in patients less than 1 year of age at diagnosis, including two renal tumors and one mediastinal soft tissue tumor. These three cases exhibited both cellular and mixed cellular and classic histology. All patients had no evidence of disease progression off therapy, despite incomplete resection. To extend our analysis and quantify the frequency of EGFR ITD in pediatric sarcomas, we retrospectively analyzed a cohort of tumors (n = 90) that were previously negative for clinical RT-PCR-based fusion testing. We identified EGFR ITD in three analyzed cases, all in patients less than 1 year of age (n = 18; 3/18, 17%). Here we expand the spectrum of tumors with EGFR ITD to congenital soft tissue tumors and report an unusual example of an EGFR ITD in a tumor with cellular congenital mesoblastic nephroma histology. We also highlight the importance of appropriate test selection and bioinformatic analysis for identification of this genomic alteration that is unexpectedly common in congenital and infantile spindle cell tumors.

Novel morphologic findings in PLAG1-rearranged soft tissue tumors.

Oncogenesis in PLAG1-rearranged tumors often results from PLAG1 transcription factor overexpression driven by promoter-swapping between constitutively expressed fusion partners. PLAG1-rearranged tumors demonstrate diverse morphologies. This study adds to this morphologic heterogeneity by introducing two tumors with PLAG1 rearrangements that display distinct histologic features. The first arose in the inguinal region of a 3-year-old, appeared well-circumscribed with a multinodular pattern, and harbored two fusions: ZFHX4-PLAG1 and CHCHD7-PLAG1. The second arose in the pelvic cavity of a 15-year-old girl, was extensively infiltrative and vascularized with an adipocytic component, and demonstrated a COL3A1-PLAG1 fusion. Both showed low-grade cytomorphology, scarce mitoses, no necrosis, and expression of CD34 and desmin. The ZFHX4-/CHCHD7-PLAG1-rearranged tumor showed no evidence of recurrence after 5 months. By contrast, the COL3A1-PLAG1-rearranged tumor quickly recurred following primary excision with positive margins; subsequent re-excision with adjuvant chemotherapy resulted in no evidence of recurrence after 2 years. While both tumors show overlap with benign and malignant fibroblastic and fibrovascular neoplasms, they also display divergent features. These cases highlight the importance of appropriate characterization in soft tissue tumors with unusual clinical and histologic characteristics.

Masked hypodiploidy: Hypodiploid acute lymphoblastic leukemia (ALL) mimicking hyperdiploid ALL in children: A report from the Children's Oncology Group.

Hyperdiploidy with greater than 50 chromosomes is usually associated with favorable prognosis in pediatric acute lymphoblastic leukemia (ALL), whereas hypodiploidy with ≤43 chromosomes is associated with extremely poor prognosis. Sometimes, hypodiploidy is "masked" and patients do not have a karyotypically visible clone with ≤43 chromosomes. Instead, their abnormal karyotypes contain 50-78 or more chromosomes from doubling of previously hypodiploid cells. When the hypodiploid and doubled hyperdiploid clones are both present, patients can be identified by traditional test methods [karyotype, DNA Index (DI), fluorescence in situ hybridization (FISH)], but the incidence of masked hypodiploid cases in which only the doubled clone is visible is unknown. We analyzed 7013 patients with B-ALL enrolled in COG AALL03B1 (2003-2011) for whom chromosome studies were available. Of 115 patients with hypodiploidy (25-39 chromosomes), karyotypes of 40 showed only the hypodiploid clone, 47 showed mosaicism with both hypodiploid and hyperdiploid (doubled) karyotypes, and 28 with masked hypodiploidy showed only a hyperdiploid (doubled) clone. Unique karyotypic signatures were identified, and widespread loss of heterozygosity (LOH) was seen in the microsatellite panel for all patients with masked hypodiploidy. An increased awareness of the unusual karyotypic profile associated with a doubled hypodiploid clone and coordinated use of DI, FISH, and LOH studies when indicated can identify patients with masked hypodiploidy and allow appropriate treatment selection.

Excellent long-term survival of children with Down syndrome and standard-risk ALL: a report from the Children's Oncology Group.

The Children's Cancer Group 1991 study was a clinical trial for children with National Cancer Institute standard-risk acute lymphoblastic leukemia (ALL). This trial demonstrated that 5 doses of vincristine and escalating IV methotrexate (MTX) without leucovorin rescue in the interim maintenance (IM) phases resulted in superior event-free survival (EFS) when compared with 2 doses of vincristine, oral (PO) MTX, PO mercaptopurine, and dexamethasone. This report describes a favorable outcome of this regimen in patients with Down syndrome (DS). Forty-four patients with DS were randomized to the arms containing PO MTX during IM, and 31 to those containing IV MTX. Ten-year EFS rates for patients with DS randomized to IV MTX vs PO MTX were 94.4% ± 5.4% vs 81.5% ± 6.6%, respectively. IV methotrexate with strict escalation parameters, as given in this study, was well tolerated, although the mean total tolerated dose received was lower in patients with DS than in those without DS. There was no increase in hepatic toxicity, systemic infections, or treatment-related deaths in patients with DS during IM on either the IV or PO MTX arms, as compared with those without DS. The incidence of mucositis was increased in patients with DS as compared with patients without DS, particularly among patients who received IV MTX. This trial was registered at www.clinicaltrials.gov as #NCT00005945.

Genomic and outcome analyses of Ph-like ALL in NCI standard-risk patients: a report from the Children's Oncology Group.

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL; BCR-ABL1-like ALL) in children with National Cancer Institute (NCI) intermediate- or high-risk (HR) ALL is associated with poor outcome. Ph-like ALL is characterized by genetic alterations that activate cytokine receptor and kinase signaling and may be amenable to treatment with tyrosine kinase inhibitors. The prevalence, outcome, and potential for targeted therapy of Ph-like ALL in standard-risk (SR) ALL is less clear. We retrospectively analyzed a cohort of 1023 SR childhood B-ALL consecutively enrolled in the Children's Oncology Group AALL0331 clinical trial. The Ph-like ALL gene expression profile was identified in 206 patients, and 67 patients with either BCR-ABL1 (n = 6) or ETV6-RUNX1 (n = 61) were excluded from downstream analysis, leaving 139 of 1023 (13.6%) as Ph-like. Targeted reverse transcription polymerase chain reaction assays and RNA-sequencing identified kinase-activating alterations in 38.8% of SR Ph-like cases, including CRLF2 rearrangements (29.5% of Ph-like), ABL-class fusions (1.4%), JAK2 fusions (1.4%), an NTRK3 fusion (0.7%), and other sequence mutations (IL7R, KRAS, NRAS; 5.6%). Patients with Ph-like ALL had inferior 7-year event-free survival compared with non-Ph-like ALL (82.4 ± 3.6% vs 90.7 ± 1.0%, P = .0022), with no difference in overall survival (93.2 ± 2.4% vs 95.8 ± 0.7%, P = .14). These findings illustrate the significant differences in the spectrum of kinase alterations and clinical outcome of Ph-like ALL based on presenting clinical features and establish that genomic alterations potentially targetable with approved kinase inhibitors are less frequent in SR than in HR ALL.

Prognostic impact of kinase-activating fusions and IKZF1 deletions in pediatric high-risk B-lineage acute lymphoblastic leukemia.

Recurrent chromosomal rearrangements carry prognostic significance in pediatric B-lineage acute lymphoblastic leukemia (B-ALL). Recent genome-wide analyses identified a high-risk B-ALL subtype characterized by a diverse spectrum of genetic alterations activating kinases and cytokine receptor genes. This subtype is associated with a poor prognosis when treated with conventional chemotherapy but has demonstrated sensitivity to the relevant tyrosine kinase inhibitors. We sought to determine the frequency of kinase-activating fusions among National Cancer Institute (NCI) high-risk, Ph-negative, B-ALL patients enrolled on Dana-Farber Cancer Institute ALL Consortium Protocol 05-001 and to describe their associated clinical characteristics and outcomes. Among the 105 patients screened, 16 (15%) harbored an ABL-class fusion (ETV6-ABL1: n = 1; FOXP1-ABL1: n = 1; SFPQ-ABL1: n = 1; ZC3HAV1-ABL2: n = 1) or a fusion activating the JAK-STAT pathway (P2RY8-CRLF2: n = 8; PAX5-JAK2: n = 4). Sixty-nine percent of patients with an identified fusion had a concomitant IKZF1 deletion (n = 11). In univariate analysis, fusion-positivity and IKZF1 deletion were each associated with inferior event-free survival; IKZF1 deletion retained statistical significance in multivariable analysis (hazard ratio, 2.64; P = .019). Our findings support therapy intensification for IKZF1-altered patients, irrespective of the presence of a kinase-activating fusion.

Targetable kinase gene fusions in high-risk B-ALL: a study from the Children's Oncology Group.

Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) is a high-risk subtype characterized by genomic alterations that activate cytokine receptor and kinase signaling. We examined the frequency and spectrum of targetable genetic lesions in a retrospective cohort of 1389 consecutively diagnosed patients with childhood B-lineage ALL with high-risk clinical features and/or elevated minimal residual disease at the end of remission induction therapy. The Ph-like gene expression profile was identified in 341 of 1389 patients, 57 of whom were excluded from additional analyses because of the presence of BCR-ABL1 (n = 46) or ETV6-RUNX1 (n = 11). Among the remaining 284 patients (20.4%), overexpression and rearrangement of CRLF2 (IGH-CRLF2 or P2RY8-CRLF2) were identified in 124 (43.7%), with concomitant genomic alterations activating the JAK-STAT pathway (JAK1, JAK2, IL7R) identified in 63 patients (50.8% of those with CRLF2 rearrangement). Among the remaining patients, using reverse transcriptase polymerase chain reaction or transcriptome sequencing, we identified targetable ABL-class fusions (ABL1, ABL2, CSF1R, and PDGFRB) in 14.1%, EPOR rearrangements or JAK2 fusions in 8.8%, alterations activating other JAK-STAT signaling genes (IL7R, SH2B3, JAK1) in 6.3% or other kinases (FLT3, NTRK3, LYN) in 4.6%, and mutations involving the Ras pathway (KRAS, NRAS, NF1, PTPN11) in 6% of those with Ph-like ALL. We identified 8 new rearrangement partners for 4 kinase genes previously reported to be rearranged in Ph-like ALL. The current findings provide support for the precision-medicine testing and treatment approach for Ph-like ALL implemented in Children's Oncology Group ALL trials.

Genomic analyses identify recurrent MEF2D fusions in acute lymphoblastic leukaemia.

Chromosomal rearrangements are initiating events in acute lymphoblastic leukaemia (ALL). Here using RNA sequencing of 560 ALL cases, we identify rearrangements between MEF2D (myocyte enhancer factor 2D) and five genes (BCL9, CSF1R, DAZAP1, HNRNPUL1 and SS18) in 22 B progenitor ALL (B-ALL) cases with a distinct gene expression profile, the most common of which is MEF2D-BCL9. Examination of an extended cohort of 1,164 B-ALL cases identified 30 cases with MEF2D rearrangements, which include an additional fusion partner, FOXJ2; thus, MEF2D-rearranged cases comprise 5.3% of cases lacking recurring alterations. MEF2D-rearranged ALL is characterized by a distinct immunophenotype, DNA copy number alterations at the rearrangement sites, older diagnosis age and poor outcome. The rearrangements result in enhanced MEF2D transcriptional activity, lymphoid transformation, activation of HDAC9 expression and sensitive to histone deacetylase inhibitor treatment. Thus, MEF2D-rearranged ALL represents a distinct form of high-risk leukaemia, for which new therapeutic approaches should be considered.

Quality assurance for Duchenne and Becker muscular dystrophy genetic testing: development of a genomic DNA reference material panel.

Duchenne and Becker muscular dystrophies (DMD/BMD) are allelic X-linked recessive disorders that affect approximately 1 in 3500 and 1 in 20,000 male individuals, respectively. Approximately 65% of patients with DMD have deletions, 7% to 10% have duplications, and 25% to 30% have point mutations in one or more of the 79 exons of the dystrophin gene. Most clinical genetics laboratories test for deletions, and some use technologies that can detect smaller mutations and duplications. Reference and quality control materials for DMD/BMD diagnostic and carrier genetic testing are not commercially available. To help address this need, the Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the genetic testing and the DMD/BMD patient communities and the Coriell Cell Repositories, have characterized new and existing cell lines to create a comprehensive DMD/BMD reference material panel. Samples from 31 Coriell DMD cell lines from male probands and female carriers were analyzed using the Affymetrix SNP Array 6.0 and Multiplex Ligation-Dependent Probe Amplification (MRC-Holland BV, Amsterdam, the Netherlands), a multiplex PCR assay, and DNA sequence analysis. Identified were 16 cell lines with deletions, 9 with duplications, and 4 with point mutations distributed throughout the dystrophin gene. There were no discordant results within assay limitations. These samples are publicly available from Coriell Institute for Medical Research (Camden, NJ) and can be used for quality assurance, proficiency testing, test development, and research, and should help improve the accuracy of DMD testing.