Chronic Myelomonocytic Leukemia (CMML) with More Than 15% of Ring Sideroblasts in Bone Marrow: An Overlapping Disorder Between CMML and Refractory Anemia with Ring Sideroblasts.

Abstract 290 The main diagnostic criteria for chronic myelomonocytic leukemia (CMML), a heterogeneous disorder sharing features of myelodysplastic syndromes (MDS) and chronic myeloproliferative disorders, is the existence of a sustained absolute monocyte count in peripheral blood (PB) above 1 × 109/L. On the other hand, the presence of more than 15% ring sideroblasts (RS) in bone marrow (BM) is a well recognized morphological feature of dyserithropoiesis and, in the absence of blasts in PB and less than 5% blasts in BM, is diagnostic of refractory anemia with ring sideroblasts (RARS) with or without multilineage dysplasia. In FAB as well as in WHO classification systems for myeloid neoplasms those cases presenting with both an absolute monocyte count in PB above 1 × 109/L and more than 15% RS in BM are diagnosed of CMML but the preeminence given to the monocyte count in PB over the proportion of RS in BM is not evidence-based. The main purpose of this study was to assess the clinical and biological characteristics and outcome [overall survival (OS) and acute leukemic (AL) evolution] of a series of 77 patients diagnosed of CMML by FAB and WHO criteria who had more than 15% RS in BM at presentation (CMML-RS) and to compare them with those of a series of 417 patients with CMML with less than 15% RS (classical CMML) and those of a series of 178 patients with classical RARS (38 patients with and 140 patients without multilineage dysplasia). Comparisons of proportions and ranks of variables between different groups were performed by chi square or Mann-Whitney-U tests as appropriate. Actuarial curves of OS and risk of AL evolution were built by Kaplan-Meier method and differences between curves compared with log-rank tests. Multivariate analyses of OS and risk of AL evolution were performed by Cox proportional hazards regression method. Patients with CMML-RS had lower hemoglobin level (P=0.008), lower absolute counts of leukocytes (P 0.90). Patients with classical RARS were more anemic (P=0.001), had lower absolute counts of leukocytes (P 1 × 109 monocytes/L in PB and >15% RS in BM should be better classified as RARS than as CMML. The WHO classification needs to be revisited to account for those findings. Disclosures: No relevant conflicts of interest to declare.