Msi-H Testing Via Hybrid Capture Based Ngs Sequencing Of Liquid Biopsy Samples.

504Background: Microsatellite instability (MSI) testing has become critically important in clinical cancer care of patients with cancer given the recent pan-tumor FDA approval of pembrolizumab for use in patients with MSI-High (MSI-H) tumors. We previously demonstrated the robustness of a novel proprietary algorithm for determination of MSI status via NGS from solid tumor biopsy specimens (J Clin Oncol 34, 2016 (suppl; abstr 1523)). Traditional MSI tests such as PCR or IHC are impractical for pan-tumor adoption, as MSI-H prevalence outside of gastrointestinal and endometrial cancers is usually u003c 1%. NGS-based ctDNA profiling provides an opportunity for both MSI and actionable alteration testing in patients in whom tissue-based biopsy is not available. Methods: Genomic DNA (gDNA) from five previously characterized MSI-H cell lines: (DLD1, 22Rv1, LNCap, RL952, CL188), and one MSS cell line (SCC9) was enzymatically-fragmented to simulate ctDNA and titrated to various dilution levels with DNA from a healthy h...