DDX41 mutations (germline and somatic) are associated with late onset myelodysplastic syndromes/acute myeloid leukemia (MDS/AML). Myeloid neoplasms (MN) with germline predisposition was identified as a distinct category in the 2016 WHO classification revision, including MN with germline DDX41 mutation. We retrospectively analyzed the molecular findings and clinical characteristics of thirty-three DDX41-mutated (mDDX41) patients at our institution. We identified 14 distinct pathogenic DDX41 variants in 32 patients and 8 DDX41 variants of unknown significance (VUS) in 9 patients. Five (16%) patients had a second DDX41 somatic mutation p.R525H and 13 (40%) had at least one additional oncogenic co-mutation in other genes. The median age at the time of diagnosis was 66 years, with male predominance (72%) and the majority of patients had normal cytogenetics (91%). Two-year overall survival (OS) was 86% and 6 (21%) MDS/AML patients with relatively preserved hematopoietic function were observed without further intervention. In comparison to AML patients with prognostically more favorable subtypes [t(8;21), n=27 and inv(16), n=40], mDDX41 patients in our cohort showed similarly favorable OS. Our study highlights that mDDX41-MN patients often have an indolent course and mDDX41-AML has comparable OS to favorable-risk AML.

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Therapy-related myeloid neoplasms (t-MN) are aggressive leukemia that develops as a complication of prior exposure to DNA-damaging agents. Clonal cytopenia of undetermined significance (CCUS) is a precursor of de novo myeloid neoplasms. Characteristics of CCUS that develop following cytotoxic therapies (therapy-related clonal cytopenia, t-CC) and outcomes following t-CC have not been described. We identified 33 patients with t-CC and compared to a cohort of the WHO-defined t-MN (n = 309). t-CC had a distinct genetic and cytogenetic profile: pathogenic variants (PV) in TET2 and SRSF2 were enriched in t-CC, whereas TP53 PV was more common in t-MN. Ten (30%) t-CC patients developed a subsequent t-MN, with a cumulative incidence of 13%, 23%, and 50% at 6 months, 1, and 5 years, respectively. At t-MN progression, 44% of evaluable patients had identifiable clonal evolution. The median survival following t-CC was significantly superior compared all t-MN phenotype including t-MDS with <5% bone marrow blasts (124.5 vs. 16.3 months, P < 0.001) respectively. The presence of cytogenetic abnormality and the absence of variants in DNMT3A, TET2, or ASXL1 (DTA-genes) were associated with a higher likelihood of developing a subsequent t-MN and an inferior survival. We describe a putative precursor entity of t-MN with distinct features and outcomes.