Garcia-Carbonero, RocioGonzález Astorga, BeatrizVidal Tocino, RosarioContreras Toledo, DéboraPericay, CarlesFernandez Montes, AnaFalcó, EstherGonzález Cordero, MartaReina Zoilo, Juan JoséAlonso, VicenteRodríguez Salas, NuriaGil-Raga, MireiaSantos, CristinaPáez, DavidAnton-Pascual, BeatrizAguilar, FernandoMorales, Pilar2023-09-272023-09-272023-08-31Garcia-Carbonero R, González Astorga B, Vidal Tocino R, Contreras Toledo D, Pericay C, Fernández Montes A, et al. Real-world study on microsatellite instability and mismatch repair deficiency testing patterns among patients with metastatic colorectal cancer in Spain. Clin Transl Oncol. 2023 Aug 31.https://hdl.handle.net/20.500.13003/19917Clinical practice guidelines recommend that all patients with metastatic colorectal cancer (mCRC) should be tested for mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H). We aimed to describe the dMMR/MSI-H testing practice in patients with mCRC in Spanish centers. Multicenter, observational retrospective study that included patients newly diagnosed with mCRC or who progressed to a metastatic stage from early/localized stages. Three hundred patients were included in the study from May 2020 through May 2021, with a median age of 68 years, and two hundred twenty-five (75%) had stage IV disease at initial diagnosis; two hundred eighty-four patients received first-line treatment, and dMMR/MSI-H testing was performed in two hundred fifty-one (84%) patients. The results of the dMMR/MSI-H tests were available in 61 (24%) of 251 patients before the diagnosis of metastatic disease and in 191 (81%) of 236 evaluable patients for this outcome before the initiation of first-line treatment. Among the 244 patients who were tested for dMMR/MSI-H with IHC or PCR, 14 (6%) were MMR deficient. The most frequent type of first-line treatment was the combination of chemotherapy and biological agent, that was received by 71% and 50% of patients with MMR proficient and deficient tumors, respectively, followed by chemotherapy alone, received in over 20% of patients in each subgroup. Only 29% of dMMR/MSI-H tumors received first-line immunotherapy. Our study suggests that a high proportion of patients with mCRC are currently tested for dMMR/MSI-H in tertiary hospitals across Spain. However, there is still room for improvement until universal testing is achieved. Not applicable.engAtribución 4.0 Internacionalhttp://creativecommons.org/licenses/by/4.0/research article10.1007/s12094-023-03309-z1699-305537651021L20251974052-s2.0-85169156775open access