3351 - Microsatellite Instability Detection in Colorectal Cancer: 44-Center Comparison between the Idylla MSI Assay and Routine Molecular and Immunohistochemistry Tests on Formalin-Fixed Paraffin-Embedded Tissue

Background

Microsatellite instability (MSI) is observed in 15% of all colorectal cancers (CRC), including Lynch syndrome caused by germline mutation of an MMR gene. Guidelines recommend assessing the MSI status of all CRC patients for screening for Lynch syndrome as well as for prognostic stratification. MSI-high tumors are more vulnerable to the immune system and therefore generally have a better prognosis.

Methods

The performance of the Idylla™ MSI Assay was compared to routine immunohistochemistry (IHC) and molecular tests (including Bethesda panel) on 1,301 archival CRC formalin-fixed, paraffin-embedded (FFPE) tissue sections, at 44 centers worldwide.

Results

The failure rate of the Idylla™ MSI Assay was 0.23%, while the molecular methods had a higher failure rate overall of 0.86% probably due to their use of a longer amplicon. IHC had a much higher failure rate of 4.37%, possibly related to interpretation difficulties of the results. Routine method failure rates might be an underestimation as the current analysis was done retrospectively on samples with known routine results. Compared to IHC, the results of 37 of the 1,075 samples tested were discordant, resulting in an overall concordance agreement of 96.6%. When taking molecular results and further analysis of discordant samples into account, the Idylla™ MSI result was confirmed in 16 samples. Compared to molecular methods, 16 of the 812 samples tested were discordant, resulting in an overall concordance agreement of 98.0%. Taking IHC results and further analysis of discordant samples into account, the Idylla™ MSI result was confirmed in 8 samples.

Conclusions

Results of the Idylla™ MSI Assay were highly concordant with results of routine tests and lower failure rates were observed. Further advantages are the lack of need for matched normal tissue, the low dependence on pre-analytical conditions, the simplified workflow, the short turnaround times, the automated result interpretation, and the very limited hands-on work.

Clinical trial identification

Editorial acknowledgement

Teams involved in the MSI, Idylla MSI Assay, Colon Rectal Cancer, Multicenter Study.

Legal entity responsible for the study

Irblleida.

Funding

Biocartis.

Disclosure

X. Matias-guiu: Non-remunerated activity/ies: Biocartis.