Detection of Microsatellite Instability in Endometrial Carcinoma Using a Novel Homopolymer Assay.

Abstract

Approximately 30% of endometrial cancers are associated with microsatellite instability (MSI) caused by deficiencies in the DNA mismatch repair (MMR) genes (dMMR). MMR testing by immunohistochemistry for MMR proteins and MSI testing by polymerase chain reaction (PCR) are routinely utilized to screen patients with colorectal cancer and endometrial cancer for Lynch syndrome and, more recently, to identify patients eligible for immunotherapy. The Biocartis Idylla™ MSI assay is a fully automated, cartridge-based real-time PCR assay. The assay uses as little as one formalin-fixed paraffin-embedded (FFPE) tumor section and is designed to detect seven novel MSI biomarkers consisting of short homopolymers located in ACVR2A, BTBD7, DIDO1, MRE11, RYR3, SEC31A and SULF2 genes. Mutation in two of these markers is considered MSI-H. FFPE of 35 ECs (25 dMMR and 10 microsatellite stable (MSS)) were used in this study. When tumor content was ≤20% on a slide, macrodissection was performed. The overall percent agreement with MMR IHC was 97% (31/32) with sensitivity = 96% and specificity = 100%. Pre-analytic evaluation of the manufacturer's recommended 20% tumor content cut-off is essential to ensure valid results. The Idylla MSI assay offers several advantages over other PCR-based assays including minimal hands-on time, rapid turn-around-time, no requirement for a paired normal sample and the use of FFPE directly without an extraction step.