A Combination of NR-21, BAT25, and MONO27 Run in One Polymerase Chain Reaction (PCR) Accurately Detects Microsatellite Instability High (MSI-H) Tumors
BP Portier, M Bronner, X Liu. Cleveland Clinic, Cleveland, OH
Background: Microsatellite instability (MSI) testing is increasingly performed on tumor tissue to screen for hereditary non-polyposis colorectal cancer. However, it remains expensive, laborious, and difficult to standardize. Several quasi-monomorphic markers were included in a MSI panel recently developed by Promega (Madison, WI). This study was undertaken to determine if the combination of three markers (NR-21, BAT25, Mono27), run in one PCR reaction, could correctly characterize MSI status in all tumors tested.
Design: The MSI database from 11/2006 to 03/2009 was reviewed. Selection criteria for MSI testing included patient age <50, right-sided colonic location, small bowel or gastric neoplasm, MSI-associated tumor morphology, and family history. The 5 marker panel of quasi-monomorphic mononucleotide repeats (BAT26, NR-21, BAT25, Mono27, and NR24) was compared to the 3-marker panel (NR-21, BAT25, Mono27) for association with MSI-H (defined as the presence of ≥ 2 unstable markers out of the 5 tested markers) or MSS (no unstable markers out of the 5 tested markers). In addition, mismatch repair protein immunohistochemistry for MLH-1, MSH-2, MSH-6, or PMS-2 was performed on 99 tumors (88 MSI-H and 11 MSS).
Results: A total of 487 tumors were tested during the study period, including 305 colorectal carcinomas, 157 colorectal adenomas, and 25 non-colorectal tumors [small bowel (13), appendix (3), stomach (2), uterus (2) and others (5)]. Out of 487 tumors tested, 10 (2.05%) had insufficient DNA. The overall MSI-H rate was 22.5% (27.6% for colorectal carcinomas, 13.3% for colorectal adenomas, and 12.4% for non-colorectal tumors). Each MSI marker, BAT26, NR-21, BAT25, Mono27, and NR-24 alone correctly identified 98%, 98%, 95%, 98%, and 96% of MSI-H tumors (N=105) and all MSS tumors (N=372). A combination of NR-21, BAT25, and Mono27 run in one PCR reaction correctly identified all 477 MSI-H and MSS tumors. Among 99 tumors (11MSS and 88 MSI-H) tested for mismatch repair proteins by immunohistochemistry, the MSI status and IHC results showed 99% concordance (1 MSI-H case failed to show loss of mismatch repair proteins by IHC).
Conclusions: A combination of NR-21, BAT25, and Mono27 (three quasi-monomorphic mononucleotide repeat markers) run in a single multiplexed PCR reaction was sufficient to determine MSI status with 100% accuracy (n=477). Whether this more limited MSI panel will reduce cost, turnaround time, or facilitate inclusion of additional molecular tests remains to be investigated.
Tuesday, March 23, 2010 9:30 AM
Poster Session III # 112, Tuesday Morning