Chronic myelomonocytic leukemia with ring sideroblasts/ SF3B1 mutation presents with low monocyte count and resembles myelodysplastic syndromes with-RS/ SF3B1 mutation in terms of phenotype and prognosis

Chronic myelomonocytic leukemia (CMML) and myelodysplastic syndromes (MDS) with ring sideroblasts (RS) or mutation (MDS-RS/ ) differ in many clinical features, but share others, such as anemia. RS and mutation can also be found in CMML. We compared CMML with and without RS/ and MDS-RS/ considering the criteria established by the 2022 World Health Organization classification. A total of 815 patients were included (CMML, n=319, CMML-RS/ , n=172 and MDS-RS/ , n=324). The percentage of RS was ≥15% in almost all CMML-RS/ patients (169, 98.3%) and most (125, 72.7%) showed peripheral blood monocyte counts between 0.5 and 0.9 x10 /L and low risk prognostic categories. CMML-RS/ differed significantly from classical CMML in the main clinical characteristics, whereas it resembled MDS-RS/ . At a molecular level, CMML and CMML-RS/ had a significantly higher frequency of mutations in (mostly multi-hit) and (p=0.013) and CMML had a significantly lower frequency of and mutations compared to CMML/MDS-RS/ . Differences in the median overall survival among the three groups were statistically significant: 6.75 years (95% confidence interval [CI] 5.41-8.09) for CMML-RS/ vs. 3.17 years (95% CI 2.56-3.79) for CMML vs. 16.47 years (NA) for MDS-RS/ , p