Validation of the fully automated IdyllaTM system for microsatellite instability detection in Chinese colorectal cancers

Abstract

Background and purpose: Microsatellite instability (MSI) and mismatch repair (MMR) defects have attracted much attention recently as one of the important biomarkers for pan-tumor immunotherapy such as colorectal cancer (CRC). Conventional methods for MSI detection with polymerase chain reaction (PCR) often require non-tumor controls as well as a long turnaround time. The IdyllaTM system as a fully automated quantitative PCR unit with a turnaround time of only 2.5 h should be proved for its reliability among Chinese CRC patients before application. Methods: Formalin-fixed paraffin-embedded (FFPE) tissue samples were collected from 87 CRC patients in Fudan University Shanghai Cancer Center from March 2017 to March 2019 and were subjected to detect MMR protein expression and MSI using immunochemistry (IHC), conventional PCR (Promega MSI analysis) and the IdyllaTM MSI system, respectively. Results: Of the 87 CRC patients enrolled, 56 cases were identified to be deficient MMR (dMMR)/MSI-high (MSI-H) and 31 to be proficient MMR (pMMR)/microsatellite stable (MSS) by both IHC and Promega MSI analysis. However, 4 cases with dMMR/MSI-H were determined to be MSS and one case with pMMR/MSS to be MSI-H using IdyllaTM MSI system, yielding a sensitivity of 92.9% (52/56), specificity of 96.8% (30/31) and an overall concordance of 94.3% (82/87). Then, the above five discordant cases were re-examined using IdyllaTM with resection tissues, as a result, four cases with ≥20% tumor contents changed to be consistent with IHC/Promega MSI assay, however, there was still one inconsistent case with only 5% tumor content. Subsequently, the case was reconfirmed using IdyllaTM with enriched tumor tissue by macrodissection, as expected, the result was demonstrated to be MSI-H, consistent with Promega MSI analysis and IHC. Furthermore, repeatability of the IdyllaTM MSI assay was proved to be reliable in 5 cases with various tumor contents (20%-60%). Conclusion: The IdyllaTM MSI system provides a fast, reliable and fully automated solution to MSI detection in Chinese CRC patients with high sensitivity, specificity and reproducibility, especially for CRC with more than 20% tumor contents.

Keywords

• |colorectal cancer|microsatellite instability|mismatch repair|idyllatm|immunochemistry|polymerase chain reaction