AUTHOR=Rodriguez Julieta E. , Vasseur Damien , Bani Mohamed Amine , Cabaret Odile , Cotteret Sophie , Muleris Martine , Golbarg Veronica , Malka David , Pudlarz Thomas , Caron Olivier , Smolenschi Cristina 

TITLE=Case report: Microsatellite instability determination is not always black and white in Lynch syndrome diagnosis

JOURNAL=Frontiers in Oncology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2024.1396869

DOI=10.3389/fonc.2024.1396869

ISSN=2234-943X

ABSTRACT=<sec><title>Introduction</title><p>Microsatellite instability (MSI) is a genetic marker that is useful in the detection and treatment of Lynch syndrome (Sd). Although conventional techniques such as immunohistochemistry (IHC) and polymerase chain reaction (PCR) are the standards for MSI detection, the advent of next-generation sequencing (NGS) has offered new possibilities, especially with circulating DNA.</p></sec><sec><title>Case report</title><p>We present the case of a 26-year-old patient with Lynch Sd and a <italic>BRAF</italic>-mutated metastatic colon cancer. The discordant MSI results between the conventional methods and NGS posed challenges in making treatment decisions. Subsequent NGS analysis revealed a high MSI status, leading to participation in an immunotherapy trial, with remarkable clinical response.</p></sec><sec><title>Conclusion</title><p>This case emphasizes the importance of comprehensive molecular profiling and strong interdisciplinary collaborations, especially in cases with ambiguous MSI results.</p></sec>