Investigation of discrepant mismatch repair immunohistochemistry and microsatellite instability polymerase chain reaction test results for gynecologic cancers using next-generation sequencing

• Published in: Human pathology 2022-01, Vol.119, p.41-50
• Main Authors: Smithgall, Marie C., Remotti, Helen, Hsiao, Susan J., Mansukhani, Mahesh, Liu-Jarin, Xiaolin, Fernandes, Helen
• Format: Article
• Language: English
• Subjects: Adult; Aged; Biomarkers; Biomarkers, Tumor - analysis; Biomarkers, Tumor - genetics; Biopsy; Databases, Factual; DNA Mismatch Repair; DNA Mutational Analysis; DNA-Binding Proteins - antagonists & inhibitors; DNA-Binding Proteins - genetics; Endometrial cancer; FDA approval; Female; Genes; Genital Neoplasms, Female - diagnosis; Genital Neoplasms, Female - enzymology; Genital Neoplasms, Female - genetics; Genital Neoplasms, Female - pathology; Gynecologic cancer; Gynecology; High-Throughput Nucleotide Sequencing; Humans; Immunohistochemistry; Immunotherapy; Laboratories; Microsatellite Instability; Middle Aged; Mismatch Repair Endonuclease PMS2 - analysis; Mismatch Repair Endonuclease PMS2 - genetics; MMR; MSI; Mutation; MutL Protein Homolog 1 - analysis; MutL Protein Homolog 1 - genetics; NGS; Oncology; Ovarian cancer; Pathology; Polymerase Chain Reaction; Predictive Value of Tests; Reproducibility of Results; Retrospective Studies; Tumors
• ISSN: 0046-8177; 1532-8392
• DOI: 10.1016/j.humpath.2021.10.004

Gynecologic cancers are routinely screened for DNA mismatch repair (MMR) gene mutations using immunohistochemistry (IHC) and/or polymerase chain reaction (PCR) for microsatellite instability (MSI) to enable selection of immune checkpoint inhibitor therapy and screen for Lynch syndrome. The limited data that compare IHC and MSI in endometrial tumors have shown discordance rates of 5–10%. We reviewed MMR/MSI results in gynecologic cancers and used next-generation sequencing (NGS) to interrogate discrepancies. Of the 328 cases with both IHC and MSI results, 256 (78.0%) were microsatellite stable (MSS) with preserved MMR (pMMR), 64 (19.5%) cases were MSI-High (MSI-H) with MMR deficient (dMMR), 2 cases showed subclonal loss of MLH1 and PMS2 with MSI-H, and 6 cases were discordant. Overall, there was a 98.2% (322/328) IHC/MSI concordance. Discordant cases were retested and/or subject to NGS. Of the six discrepant cases, five showed dMMR with MSS and one showed pMMR with MSI-H. One dMMR/MSI-L case showed loss of PMS2 with a germline pathogenic mutation. The pMMR/MSI-H case was found to harbor pathogenic variants in MLH1 and MSH6. One of the two cases with subclonal populations demonstrated MSI-H in the dMMR area and MSS in the pMMR area. These results emphasize the importance of selecting the appropriate tumor tissue for both IHC and molecular testing and demonstrate that NGS can help resolve discrepant MMR and MSI results. •Gynecologic cancers show high concordance rate between MMR IHC and MSI PCR overall.•Subclonal loss of MMR proteins can lead to IHC/MSI discrepancies.•Selection of appropriate tumor and normal tissue for IHC and MSI testing reduces discrepancies.•NGS can help resolve MMR and MSI discordance.