Validation of Microsatellite Instability Detection Using a Comprehensive Plasma-Based Genotyping Panel.

Purpose: To analytically and clinically validate microsatellite instability (MSI) detection using cell-free DNA (cfDNA) sequencing.

Experimental Design: Pan-cancer MSI detection using Guardant360 was analytically validated according to established guidelines and clinically validated using 1,145 cfDNA samples for which tissue MSI status based on standard-of-care tissue testing was available. The landscape of cfDNA-based MSI across solid tumor types was investigated in a cohort of 28,459 clinical plasma samples.