biostudies-literatureCrisafulli GBiLiGeCT—Progetto PONCancer Research UKEuropean Union's Horizon 2020AIRCFC AECC1656-1675https://www.ebi.ac.uk/biostudies/studies/S-EPMC9394384biostudies-literatureUnknown12(7)The majority of metastatic colorectal cancers (mCRC) are mismatch repair (MMR) proficient and unresponsive to immunotherapy, whereas MMR-deficient (MMRd) tumors often respond to immune-checkpoint blockade. We previously reported that the treatment of colorectal cancer preclinical models with temozolomide (TMZ) leads to MMR deficiency, increased tumor mutational burden (TMB), and sensitization to immunotherapy. To clinically translate these findings, we designed the ARETHUSA clinical trial whereby O6-methylguanine-DNA-methyltransferase (MGMT)-deficient, MMR-proficient, RAS-mutant mCRC patients received priming therapy with TMZ. Analysis of tissue biopsies and circulating tumor DNA (ctDNA) revealed the emergence of a distinct mutational signature and increased TMB after TMZ treatment. MultipCancer discoveryTemozolomide Treatment Alters Mismatch Repair and Boosts Mutational Burden in Tumor and Blood of Colorectal Cancer Patients.PMC9394384A26825101020342ARS01_00492A2822322795GEACC18004TABSiena SCassingena ABardelli APietrantonio FGermano GCrisafulli GMacagno MBonoldi ELazzari LValtorta EBattuello PIdotta LBartolini ALuraghi PPersoneni NSartore-Bianchi AMarsoni SMauri GAmatu AVitiello PPMorano FPessei VBarault LZampino MGDi Nicolantonio FTosi FfalseTemozolomide Treatment Alters Mismatch Repair and Boosts Mutational Burden in Tumor and Blood of Colorectal Cancer Patients.The majority of metastatic colorectal cancers (mCRC) are mismatch repair (MMR) proficient and unresponsive to immunotherapy, whereas MMR-deficient (MMRd) tumors often respond to immune-checkpoint blockade. We previously reported that the treatment of colorectal cancer preclinical models with temozolomide (TMZ) leads to MMR deficiency, increased tumor mutational burden (TMB), and sensitization to immunotherapy. To clinically translate these findings, we designed the ARETHUSA clinical trial whereby O6-methylguanine-DNA-methyltransferase (MGMT)-deficient, MMR-proficient, RAS-mutant mCRC patients received priming therapy with TMZ. Analysis of tissue biopsies and circulating tumor DNA (ctDNA) revealed the emergence of a distinct mutational signature and increased TMB after TMZ treatment. Multip2022-01-01T00:00:00Z2022 Jul2026-07-14T21:12:19.772Z2025-04-06T14:12:25.022ZS-EPMC93943843552227310.1158/2159-8290.CD-21-1434