No increase of targetable oncogenic fusions prevalence in non-colorectal mismatch repair-deficient tumors

Mismatch repair deficiency is a well-described mechanism of carcinogenesis, which can be identified by microsatellite instability (MSI). In colorectal cancers (CRC), cases with hypermethylation of the MLH1 promoter with wild-type (WT) BRAF /RAS status show a high prevalence of oncogenic fusions, notably those involving NTRK. NTRK fusions can be targeted by TKIs. In CRC, MSI phenotype combined with WT BRAF/RAS status allows for improved screening of patients who could benefit from this treatment. In this study, we aimed to verify if the correlation observed in CRC was valid for other MSI tumors and if this screening method could thus be extended to other cancers. We conducted an analysis on a control cohort of 23 selected CRC and identified 5 fusions, 4 of which involved NTRK1. However, no fusions were found in the cohort of 100 non-colorectal MSI tumors.