A Simple Blood Test for Microsatellite Instability Status

Abstract Immune checkpoint inhibitorICIimmunotherapeutics are having an important and expanding impact on the treatment of cancerAfter only a few years of clinical useICIs have become a multi billion dollar family of productsHoweveronlyof patients have a positive response to treatmentTo datethe best indicator for a positive response is the microsatellite instabilityMSIstatusIndividualsno matter what the cancer typethat are MSI High have as high aspositive response rateHoweverto date only cancers with a high frequency of MSI He gcolon cancerare routinely screened for MSI statusHoweverthe high positive response rate of MSI H patients has led to the urging that all cancers be screened for MSI statusRoche and Merck have just announced plans to develop a test to do soThey will pursue one of the two standard assaysimmunohistochemistryIHCin which tumor sections are stained for presence ofproteins involved in mismatch repairThe other is PCR oflong MSs to determine if there is an insertion or deletion of a baseWe propose a fundamentally different strategySince the determining immunological outcome of MSI is the production of frameshift peptideswe will measure the patientandapos s immune reactivity against allpossible tumor produced FS peptidesFSPusing a propriety peptide microarray containing all possible FSPsThis simple assay uses a small volume of blood as opposed to a tumor biopsyand by measuring the antibodies produced against the FS peptidesprovides a rapidaccurate scoring of MSI statusThis would afford the possibility of inexpensively and simply determining the MSI status for all cancer patients from a small amount of blood Project Narrative Microsatellite instabilityMSIis a clinically approved diagnostic to rule in patients for treatment with immune checkpoint inhibitor therapiesHoweverthis assay currently requires a tumor biopsyis complex and is only recommended for cancers with high rates of MSIsuch as colon cancerWe have developed a blood based assay that can determine MSI status without a biopsy and will test its performance in this project