J Pathol Transl Med.  2019 Nov;53(6):386-392. 10.4132/jptm.2019.09.25.

Clinical Utility of a Fully Automated Microsatellite Instability Test with Minimal Hands-on Time

Affiliations
  • 1Department of Pathology, University of Ulsan College of Medicine, Seoul, Korea. jihunkim@amc.seoul.kr
  • 2Asan Center for Cancer Genome Discovery, University of Ulsan College of Medicine, Seoul, Korea.
  • 3Department of Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.

Abstract

BACKGROUND
Microsatellite instability (MSI) analysis is becoming increasingly important in many types of tumor including colorectal cancer (CRC). The commonly used MSI tests are either time-consuming or labor-intensive. A fully automated MSI test, the Idylla MSI assay, has recently been introduced. However, its diagnostic performance has not been extensively validated in clinical CRC samples.
METHODS
We evaluated 133 samples whose MSI status had been rigorously validated by standard polymerase chain reaction (PCR), clinical next-generation sequencing (NGS) cancer panel test, or both. We evaluated the diagnostic performance of the Idylla MSI assay in terms of sensitivity, specificity, and positive and negative predictive values, as well as various sample requirements, such as minimum tumor purity and the quality of paraffin blocks.
RESULTS
Compared with the gold standard results confirmed through both PCR MSI test and NGS, the Idylla MSI assay showed 99.05% accuracy (104/105), 100% sensitivity (11/11), 98.94% specificity (93/94), 91.67% positive predictive value (11/12), and 100% negative predictive value (93/93). In addition, the Idylla MSI assay did not require macro-dissection in most samples and reliably detected MSI-high in samples with approximately 10% tumor purity. The total turnaround time was about 150 minutes and the hands-on time was less than 2 minutes.
CONCLUSIONS
The Idylla MSI assay shows good diagnostic performance that is sufficient for its implementation in the clinic to determine the MSI status of at least the CRC samples. In addition, the fully automated procedure requires only a few slices of formalin-fixed paraffin-embedded tissue and might greatly save time and labor.

Keyword

Microsatellite instability; Polymerase chain reaction; Idylla MSI test; Diagnostic performance; Tumor purity

MeSH Terms

Colorectal Neoplasms
Microsatellite Instability*
Microsatellite Repeats*
Paraffin
Polymerase Chain Reaction
Sensitivity and Specificity
Paraffin

Figure

  • Fig. 1. Sample processing protocol depending on the tumor purity and tissue surface area. FFPE, formalin-fixed paraffin-embedded.

  • Fig. 2. Details of three cases with discrepant results between the Idylla microsatellite instability (MSI) assay and the standard polymerase chain reaction (PCR) test. (A–C) Case No. 28, MSI-high (MSI-H) according to the Idylla MSI assay. Standard PCR MSI test is consistent with microsatellite stable (MSS) (A). MSH2 and MLH1 expression is shown in immunochemical staining (B), and next-generation sequencing (NGS) results show MSS pattern (C). (D–F) Case No. 131, MSS (0/7) according to the Idylla MSI assay. Two markers show instability in standard PCR MSI test (arrows, D), and MSH6 and PMS2 protein expressions are shown (E). Repeated NGS shows MSS pattern (F). (G, H) Case No. 133, MSS (0/7) according to the Idylla MSI assay. Two markers show instability in standard PCR MSI test (arrows, G), and MSH6 and PMS2 expressions are shown (H). Repeated NGS analysis was failed. Mutation load, the number of total somatic mutations detected by our NGS panel; TMB, tumor mutation burden, the inferred number of somatic mutations per megabase; I index, the number of insertion or deletion mutations divided by the number of all mutations; IHC, immunohistochemistry


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