Validation of blood tumor mutation burden in Labcorp Plasma Complete

Introduction: Tumor mutation burden (TMB) is an important and clinically relevant genomic signature for guiding physicians towards immunotherapies for their cancer patients. Blood TMB (bTMB) represents a potential method to measure TMB in cancer patients via blood-based liquid biopsy testing. Labcorp Plasma Complete™ (LPC) is a laboratory developed test (LDT) that analyzes circulating tumor DNA (ctDNA) to identify genomic alterations in cancer without the need for an invasive tumor tissue biopsy. In this study, we demonstrate that LPC can successfully and reproducibly report bTMB using a cohort of 84 clinical plasma samples compared to an orthogonal LDT. Methods: Sequencing libraries were generated using 25ng of cell-free DNA (cfDNA) from 84 unique plasma samples originating from individuals diagnosed with varying solid cancer types. bTMB values from LPC were compared to bTMB values from an orthogonal test. A subset of 6 samples with a range of bTMB values reported by the orthogonal test were processed in triplicate across multiple operators and sequencing instruments to demonstrate reproducibility of the bTMB value reported by LPC. The standard deviation and average positive and negative agreement (APA and ANA) of the bTMB values were assessed based on bTMB-high and bTMB-not high status between all evaluable replicates. Specificity was assessed in 20 non-cancerous plasma samples to determine how many observations had a higher bTMB value than the established limit of blank. Results: Concordance of bTMB values between LPC and the orthogonal test demonstrated a Pearson correlation coefficient of 0.78. LPC reported bTMB values from 0-37.13 mutations/Mb and samples were categorized as bTMB-high if the value was ≥7 mutations/Mb by LPC and ≥15 mutations/Mb by the orthogonal. Lower bTMB values were categorized as bTMB-not high, resulting in a positive percent agreement (PPA) of 100% and negative percent agreement (NPA) of 97.5%. Samples processed for reproducibility purposes demonstrated a 100% APA and 100% ANA with an average standard deviation of 0.94 mutations/Mb. Conclusions: Utilizing the highly trained bTMB algorithm, LPC can produce accurate and reproducible bTMB values. The addition of this molecular signature to LPC will help guide physicians towards immunotherapy options, and the added utility will enable a more comprehensive precision oncology strategy for cancer patients.