Novel Biocartis Idylla™ cartridge-based assay for detection of microsatellite instability in colorectal cancer tissues.

Introduction: Current methods to detect mismatch repair (MMR) status of colorectal cancer include immunohistochemistry (IHC) and molecular analysis of microsatellite instability (MSI) markers. In this study, we evaluated the performance of a novel Biocartis Idylla™ MSI cartridge-based assay.

Methods: The Biocartis Idylla™ MSI Assay determines MSI status using seven homopolymers frequently mutated in MSI-H cancers. We tested 47 formalin-fixed paraffin-embedded (FFPE) colon cancer tissues previously characterized for MMR deficiency by IHC at our institution from 2013 to 2018. These included 23 MMR-proficient carcinomas with positive/retained nuclear staining of MLH1, PMS2, MSH2, and MSH6 proteins and 24 MMR-deficient carcinomas with loss of nuclear staining for at least one of these proteins. Five μm thick tissue sections were collected from FFPE tissue blocks for each tumor, and the tumor regions were macrodissected, run on the Idylla™ instrument and compared with the Promega panel result. In addition, we evaluated the precision and LOD by using a MSI-H commercially available control and MSS patient samples. A positive result was considered MSI-H when two or more mutations were detected.

Results: The overall percent agreement among MMR IHC, the Idylla™ and Promega MSI assays was 100% (47/47). The agreement was 100% in both IHC-determined MMR-proficient tumors (23/23) and IHC-determined MMR-deficient tumors (24/24), compared with molecular MSI assays.

Conclusion: The novel Biocartis Idylla™ cartridge-based MSI assay showed complete concordance with MMR IHC status and Promega MSI assay. These findings support the use of the Biocartis Idylla™ cartridge-based MSI assay as a rapid and cost-effective alternative method to determine MMR status.