# Microsatellite Instability (MSI)

It is recommend to calculate MSI in [tumor-only mode](https://help.dragen.illumina.com/product-guide/dragen-v4.4/dragen-dna-pipeline/biomarkers/biomarker-msi#example-command-for-tumor-only-mode). Tumor-only mode relies on a reference directory of files (.dist) containing the microsatellite repeat distribution in a panel of normals. Both the reference directory and microsatellite list are provided - see the [Resource Files page](https://help.ffpe-exomev2p5.illumina.com/resource-files) for more information - and need to match the reference genome used in the alignment step.