Discrepancy among microsatellite instability detection methodologies in non-colorectal cancer: Report of 3 cases

• Published in: World journal of clinical cases 2023, Vol.11 (13), p.3105-3113
• Main Authors: Şenocak Taşçı, Elif, Yıldız, İbrahim, Erdamar, Sibel, Özer, Leyla
• Format: Report
• Language: English
• ISSN: 2307-8960; 2307-8960
• DOI: 10.12998/wjcc.v11.i13.3105

BACKGROUNDMicrosatellite instability (MSI) is a predictive biomarker for cancer immunotherapy. The tumor-agnostic nature of MSI makes it a denominator for immunotherapy in several solid tumors. It can be assessed using next-generation sequencing (NGS), fluorescent multiplex PCR, and immunohistochemistry (IHC). CASE SUMMARYHere, we report 3 cases with discordant MSI results detected using different methods. A cholangiocellular carcinoma case revealed proficient mismatch repair (MMR) by IHC but high MSI (MSI-H) by liquid NGS. A cervical cancer case revealed deficient MMR by IHC, microsatellite stable by PCR, and MSI-H by NGS. Lastly, an endometrial cancer case revealed proficient MMR by IHC but MSI-H by NGS. CONCLUSIONIHC for MMR status is the first choice due to several advantages. However, in cases of indeterminate IHC results, molecular testing by MSI-PCR is preferred. Recently, NGS-based MSI assays are being widely used to detect MSI-H tumors. All three methods have high accuracy; however, the inconsistencies between them may lead to misdiagnosis.