[682] Can a Three-Marker Panel (NR-21, BAT-25 and MONO-27) Accurately Detect Microsatellite High (MSI-H) Colorectal Tumors without Control DNA?

Deepa T Patil, Mary P Bronner, Thomas P Plesec, Cory R Fraser, Xiuli Liu. Cleveland Clinic

Background: Microsatellite testing (MSI) testing is performed on tumor samples to screen for Lynch Syndrome (LS). Previously, we demonstrated that a 3-marker panel of NR-21, BAT-25, and MONO-27 (Promega MSI kit) accurately determines MSI status when read with paired control DNA {Portier BP 2009}. This study was undertaken to determine if this 3-marker panel without paired control DNA accurately detects MSI-H tumors.
Design: A total of 478 MSI tests performed were divided into a test group [colorectal cancer (CRC),n=172] and a validation group (179 CRCs,127 adenomas). The size of control alleles for each marker from the test group was recorded, their mean and median size calculated, and a range (median size ± 3 bp) was generated. Each marker was considered unstable either when the difference between tumor allele and mean control allele size (generated from test group) was ≥3 bp or when the tumor allele size was beyond the range generated from test group. Using the 3-marker panel, a tumor was interpreted as MSI-H when ≥ 1 marker was found to be unstable. The performance of this panel was compared to the 5-marker panel with control non-tumor DNA; MSI-H defined as ≥ 2 unstable markers (gold standard).
Results: In the test group, the mean size of normal alleles for NR-21, BAT-25 and MONO-27 was 101, 124, and 152 bp; their median and range were 102 and 99-105 bp, 124 and121-127 bp, 152 and 149-155 bp, respectively. Overall, this 3-marker panel identified all MSI-H tumors but overcalled 2.7% cases (mean ± 3 bp) and 3.3% cases (median size ± 3 bp) of MSS tumors as MSI-H.

   Compared to 5-marker panel 
 MSI-HMSSSensitivity (%)Specificity (%)
Test group (n=172)    
5-markers + control DNA36136--
3-markers (mean ± 3 bp)4013210097
3-markers(median ± 3 bp)4312910095
Validation group(n=306)    
5-markers + control DNA47259--
3-marker (mean ± 3 bp)5225410098
3-markers(median ± 3 bp)5623910096
Entire cohort (n=478)    
5-markers + control DNA83395--
3-markers (mean ± 3 bp)9638210097
3-markers (median ± 3 bp)9937910096



Conclusions: This 3-marker panel simplified from the Promega MSI kit with MSI-H defined as ≥ 1 unstable marker, without paired control DNA, determines MSI status with 100% sensitivity. The rare false positive cases can be clarified either by mismatch repair protein immunohistochemistry or by repeating PCR with paired control DNA. This approach will miss extremely rare non-monomorphic alleles, but will greatly decrease the MSI testing cost and facilitate universal LS screening in CRCs.
Category: Gastrointestinal

Monday, February 28, 2011 8:45 AM

Platform Session: Section E, Monday Morning

 

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