Abstract Background: Molecular characterization of tumor and/or host has the potential to advance the management of pediatric cancer and high risk hematologic disease, but the clinical utility of integrating genomic profiling into standard clinical practice has been limited. The PIPseq Program at Columbia University has instituted prospective CLIA-compliant genomic sequencing for newly diagnosed, high risk, relapsed or refractory pediatric cancer patients and patients referred for bone marrow transplantation. Methods: Families are consented for clinical cancer whole-exome sequencing (cWES) or constitutional whole-exome sequencing (WES) with opt out options for return of results, exclusion of results from medical records, receipt of American College of Medical Genetics (ACMG) recommended secondary germline variants, and data/ sample use in research. Molecular characterization utilizes next generation cWES, WES, RNAseq (transcriptome), or targeted sequencing of select cancer genes. Clinical cancer reports include: known tumor type-specific actionable somatic mutations (Tier 1); somatic mutations actionable in other tumor types, in targetable pathways, or in well-established cancer genes (Tier 2); other somatic mutations in cancer genes (Tier 3); and somatic variants of uncertain significance (VUS; Tier 4). Reports for cWES testing also note translocations, significantly over expressed genes, segmental copy number variation, and germline variants. Institutional Review Board approval was obtained to conduct a retrospective review of results to date. Five categories were developed to assess clinical utility and describe significance: 1) diagnostic, 2) prognostic, 3) potentially actionable target, 4) other critical role in decision making, and 5) implications for health maintenance and genetic counseling. Results: Since January 2014, adequate tissue samples were available for 47 patients, including 31 (66%) with solid tumors and 16 (34%) with hematologic conditions. Testing included cWES (n=8), cWES with transcriptome (n=15), transcriptome only (n=1), targeted somatic panel (n=8), constitutional WES only (n=6), and multiple sequencing platforms (n=7). Normal tissue was obtained from buccal swab (n=8), blood (n=18), and unaffected tissue (n=1). Three families opted out of receiving secondary findings. Genomic aberrations were reported in 41/47 patients. Of the 127 cancer alterations found, 70 (55%) were in 15 patients with hematologic disease (median 2, range 1-11) and 57 (45%), were in 26 patients with solid tumors (median 1, range 1-6). Among the hematologic cases, alterations of known or potential clinical relevance were categorized as Tier 1 (n=0), Tier 2 (n=27), Tier 3 (n=2) mutation, or translocation (n=4); whereas in solid tumors these were categorized as Tier 1 (n=1), Tier 2 (n=14), Tier 3 (n=3) mutation, or translocation (n=9). Twenty-four Tier 4 somatic VUS were identified in hematologic specimens and 26 in solid tumor specimens. Genomic interrogation informed diagnosis in 10 patients (3 previously unknown); provided new prognostic information in 4; identified potentially actionable targets in 15; influenced clinical decision making regarding bone marrow transplant in 2; and revealed cancer or other disease predisposition in 7. Secondary germline ACMG findings in BRCA1 and PMS2 were found. Germline APC mutation was confirmed in one patient and germline VUS in SDHC was seen in another. Novel germline findings were also observed in RUNX1, MLL2 and DICER1. Overall, the PIPseq platform provided clinically impactful results in 30/47 cases (64%). Conclusions: Utilizing a CLIA-compliant prospective WES-based platform, more than half of selected patients derived clinically impactful information. The potential clinical utility of genomic sequencing in pediatric hematology-oncology has likely been underestimated. This abstract is also presented as Poster 50. Citation Format: Julia L. Glade Bender, Jennifer A. Oberg, Maria Luisa Sulis, Filamon Dela Cruz, Anthony N. Sireci, Susan J. Hsiao, Darrell J. Yamashiro, Carrie Koval, Wendy K. Chung, Stephen G. Emerson, Rebecca Zylber, Samantha Cano, Danielle P. Denney, Stuart Andrews, Peter L. Nagy, Mahesh M. Mansukhani, Andrew L. Kung. Precision in Pediatric Sequencing (PIPseq): Clinical implementation of genomic sequencing into pediatric hematology-oncology practice. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr PR01.