Revision of interpretation criteria to define microsatellite instability in mismatch repair–deficient neoplasms with subtle electropherogram changes
Abstract
Objectives
To improve analytic performance characteristics of a microsatellite instability (MSI-V1.2) assay in endometrial cancers (ECs).
Methods
Nonneoplastic and neoplastic DNA from colorectal cancers (CRCs) and ECs were compared to define MSI by calculating base shifting of the highest peak and the 5% peak (the leftmost peak with a peak height >5% of the highest peak).
Results
We first demonstrated highly precise sizing by capillary electrophoresis. However, relative intensity of multiple peaks, characteristic for microsatellite amplicons, might show a 1-base, but not a 2-base or more, shift of the highest or 5% peak among duplicate runs of nonneoplastic DNA. This inherent bias of the polymerase chain reaction–based MSI assay may lead to false-positive interpretation if MSI was defined by a 1-base shift or more. Subsequently, MSI was evaluated by a 2-base shift or more of the highest peak (original criteria) or a 2-base shift or more of either the highest or 5% peak (revised criteria) without subjective interpretation of a subtle change of electropherogram configuration (the so-called shoulder pattern). While both criteria were highly sensitive in CRCs, the revised criteria improved sensitivity (83% vs 67%) and accuracy (89% vs 79%) and maintained 100% specificity in ECs.
Conclusions
The revised criteria provided sensitive, specific, and objective interpretation to examine subtle changes of MSI.