Big data collected in large international cooperations now allow validation of findings from traditional national patient cohorts for proving consistency. In this study, we compared findings in RUNX1-mutated patients of the Austrian biodatabase for chronic myelomonocytic leukemia (ABCMML) with the CMML cohort documented in cBioPortal. In the cBioPortal cohort, RUNX1-mutated patients had significantly inferior survival and AML-free survival as compared to nonmutated patients. In the ABCMML cohort, survival and AML-free survival were numerically shorter in RUNX1-mutated patients than in wildtype patients, but this did not reach significance. Regarding phenotype, in both cohorts, RUNX1-mutated patients had a significantly higher proportion of patients with thrombocytopenia and lower metric values for platelets as compared to wildtype patients. Validation of data, as we have done in this study in CMML patients using two independent cohorts, ensures the quality standards that are required for their use in clinical decision making.