[1844] High Frequency of Instability in Penta D in Microsatellite Instability High Colorectal Cancer: Potential Pitfall in Tumor DNA Identity Interpretation.

Melissa A Grilliot, Mary Bronner, Deepa Patil, Thomas Plesec, Xiuli Liu. Cleveland Clinic

Background: DNA fingerprinting analysis was originally developed for parental and forensic identity testing using normal tissue. However, it has been increasingly used to confirm identity in possible malignant tissue contaminants on histologic slides or in cases of mislabeled tissue blocks. The Promega PowerPlex 16 System is widely used for tumor DNA fingerprinting and analyzes 15 polymorphic microsatellite loci, including Penta D. This allele is also present in the widely used Promega microsatellite instability (MSI) kit. Penta D instability may lead to false positive non-identity results in MSI-H cancers. This study aims to determine the frequency of Penta D instability in MSI-H colorectal cancers and to raise pathologists' awareness of potential pitfalls in tumor DNA identity interpretation.
Design: Electropherograms for MSI tests performed on colorectal neoplasms from 2009 to 2010 were retrieved. All alleles of Penta D in tumors were recorded and compared to paired normal control tissue to determine the frequency of altered alleles and overall pattern of alleles in MSI-H tumors. MSI-H was determined using the Promega MSI kit in context with paired normal control.
Results: Electropherograms for MSI tests performed on 473 colorectal neoplasms were analyzed. A total of 79 tumors were MSI-H and 394 were microsatellite stable (MSS). Of 79 MSI-H neoplasms, 37 (46.8%) revealed instability in Penta D [vs. 1 of 394 (0.3%) MSS tumors, p<0.00001]. In MSI-H tumors with Penta D instability, 22 cases (59.5%) had 3 Penta D peaks, 5 cases (13.5%) had 4 peaks, 7 cases (18.9%) with homozygous Penta D control DNA showed 2 peaks, and other patterns were seen in 3 cases (7.6%).
Conclusions: Penta D instability is common in MSI-H tumors (46.8%); its presence produces a mixed or nonidentity genotype pattern in comparison to known patient DNA. Without attention to this fact, Penta D instability in MSI-H tumor could result in false positive DNA non-identity test results. The rate of instability in MSI-H tumors of the remaining 14 loci comprising the Promega PowerPlex 16 System kit, in addition to Penta D are urgently needed to further address this largely unrecognozided issue.
Category: Quality Assurance

Monday, February 28, 2011 1:00 PM

Poster Session II # 229, Monday Afternoon


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