Mutational Spectrum and Clinical Outcomes of Myelodysplastic/Myeloproliferative Neoplasms: A Single-Institution Study in Korea with Emphasis on U2AF1

Background: Myelodysplastic/myeloproliferative neoplasms (MDS/MPNs) are rare hematopoietic disorders that exhibit overlapping pathological and molecular features of both MDS and MPN. This study aimed to investigate the mutational profiles and prognostic implications of MDS/MPN subtypes in Korean patients. Methods: We retrospectively reviewed 53 patients with MDS/MPN who underwent bone marrow examination and next-generation sequencing panel testing. Overall survival was analyzed with 3-year censoring. The cohort included chronic myelomonocytic leukemia (CMML; N = 30); MDS/MPN with neutrophilia (N = 6); MDS/MPN with SF3B1 mutation and thrombocytosis (N = 4); and MDS/MPN, not otherwise specified (MDS/MPN-NOS; N = 13). Results: The most frequently mutated gene was ASXL1 (52.8%), followed by TET2 (39.6%) and U2AF1 (18.9%), in total MDS/MPN. U2AF1 mutations were particularly frequent in myelodysplastic CMML (33.3%) and MDS/MPN-NOS (30.8%). In CMML, ASXL1 and TET2 mutations were associated with a trend toward better prognosis compared with wild-type (HR 0.21, p = 0.052; HR 0.25, p = 0.057, respectively), while U2AF1 mutations were associated with adverse prognosis in univariate analysis with borderline significance (HR 12.20, p = 0.050). Clinical/Molecular CMML-Specific Prognostic Scoring System and Mayo Molecular Model showed stepwise survival patterns across risk groups without statistical significance. In univariate analysis, transfusion dependency was associated with poor prognosis (HR 7.78, p = 0.013). Conclusions: This study provides the first single-institution analysis in Korean patients with MDS/MPN and identified U2AF1 mutations as a potentially significant prognostic factor, enhancing the molecular understanding of MDS/MPN.