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Microsatellite Instability (MSI)

Hi,

Could anyone suggest me free tools for calculating MSI for tumor samples alone?

TIA

next-gen sequencing

2 answers

You can use MSIsensor

Tumor only mode :

# first scan genome of interest 
msisensor scan -d reference.fa -o microsatellites.list
# Then use tumor bam file to detect MSI 
msisensor msi -d microsatellites.list -t tumor.bam -e bed.file -o output.tumor.prefix

Hey Nicolas, Thanks for the reply. I have already used MSIsensor for 3 tumor samples. But I get 0 for "Number of sites with enough coverage" and "Number of somatic sites". How should I work further with MSIsensor?

You should edit your question to add more informations regarding your data (which type : WGS, WES, targeted, etc... ). Without that I (and the community) would not be able to help you more.

Yeah, sorry about that. I have used MSIsensor for 3 different tumor exome samples without matched normal and getting 0 as the value for "Number of sites with enough coverage" and "number of somatic sites (%)" for all the 3 samples. I need to know whether the value I'm getting is correct or am I missing out on something.

Maybe check some sites in IGV to look if coverage is really low .. You could also reduce coverage thresold in msisensor mis with -c <int> coverage threshold for msi analysis, WXS: 20; WGS: 15, default=20

I had set the coverage threshold to -c 20 but I still get the output as 0. Below is the code I've used, kindly let me know if I've done it the right way:

msisensor msi -d microsatellites.list -c 20 -i 1 -t tumor.bam -e bed.file -o output.tumor.prefix

And. I'll also check some sites with IGV.

-c 20 is the default for WES. To decrease to min 10 of coverage try with -c 10

I changed it to 10 and then increased the coverage as well. I'm still getting 0.

Hi, Output of a tumor only case, is 2144 3491 15.01. I have a few queries regarding it.

1.From the sample output given on the github page, I understand that 15.01 is the % of "Number of somatic sites" and is the msi score as well. Is it msi-high or msi-low? 2. What is the cutoff score? Because it is mentioned that the cutoff values are calculated for various cancer types. 3.How do I get the MSI status?

TIA

Hey, Thanks for the article. I have read it. Let me explain from what I understood from the graph is, <10% would be msi-low and >10% is msi-high. Did I get it right?

Yes indeed but should execute msisensor on all your samples and then check if you can see some stratification. Even better test it on control samples

Okay will do it. Thank you so much.

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