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

  • 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.


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.
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.
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.
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.


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

MeSH Terms

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