Detection of Microsatellite Instability in Colorectal Cancer Tissue and Plasma samples using a new Multiplex Droplet Digital PCR kit

Management of colorectal cancer (CRC) patients relies on the accurate determination of microsatellite instability (MSI) status. MSI status can have an influence on therapy decisions centered on immune checkpoint inhibitors. In this study a novel droplet digital PCR (ddPCR) kit for MSI status determination was validated across 2 separate CRC patient cohorts: 102 tumor samples from the ALGECOLS cohort and 129 plasma samples from the RASANC cohort. Each cohort was assessed for MSI status using the novel ddPCR kit and compared to historical and/or newly obtained results, (either immunohistochemistry analysis or PCR amplification). Concordance between ddPCR and conventional MSI determination methods for the analysis of tissue samples was 97.1% for ALGECOLS. When looking at positive ctDNA samples, a strong concordance was observed for the RASANC cohort. This study illustrates that ddPCR MSI testing represents a rapid, sensitive and accurate method with a strong correlation to established methods. Moreover, the ability of the described approach to monitor MSI status in both tumor and plasma enhances the potential for the use of MSI status in longitudinal monitoring of CRC patients.