Prognostic Value of a New Clinically-Based Classification System in Patients with CMML Undergoing Allogeneic Hematopoietic Stem Cell Transplantation: A Retrospective Analysis of the EBMT Chronic Malignancies Working Party

Introduction: A new 3-group clinical classification schema proposed by the International Consortium (Blood 2016,128:4320) and subsequently validated by the MDS Düsseldorf Registry (Leukemia Research 2017,55:S149) was shown to independently stratify Chronic Myelomonocytic Leukemia (CMML) patients with regard to prognosis. The groups were defined as follows: 1. Myelodysplastic (MD)-CMML: WBC ≤10 x 109/L, circulating immature myeloid cells (IMC) = 0, no splenomegaly; 2. MD/MP (overlap) -CMML: WBC 10-20 x 109/L or WBC ≤10 x 109/L but IMC>0 and/or splenomegaly; 3. Myeloproliferative (MP)-CMML: WBC >20 x 109/L. The aim of this study was to determine the impact of this new classification schema on the outcome of allogeneic hematopoietic stem cell transplantation (HSCT), still representing the only curative option for eligible patients with CMML. Since time from diagnosis to transplant is highly variable with clinical data being highly dependent both on the disease natural history and on pretransplant treatments, in this study the group classification was based on the data registered at time of transplantation. Patients and Methods: Patients who had received a first allogeneic HSCT for CMML between 1997 and 2016 were selected from the EBMT database. Following the exclusion of patients transformed into AML at the time of transplant, 1614 patients were initially included. However, since information on spleen assessment was reported only in 9.4% of patients (with splenomegaly in 22.5% of them), the final number of patients included in the analysis, with IMC replaced by peripheral blasts (PB), was 151. Survival of this group of patients and the remaining 1463 for whom spleen, WBC and PB data were not reported were almost identical, therefore validating the assumption that the study population included in the analysis was representative of the whole study population with respect to survival. Impact of the new classification on HSCT outcome was analyzed regarding OS and PFS, cumulative incidence of relapse and NRM (gray test). Results: 98 male (64.9%) and 53 female (35.1%) patients were included to the study. Median age at HSCT was 60 years (range 20-75). At time of HSCT, 39 (26.2%) patients were in complete remission, whereas 110 (73.8%) had active disease (2 missing). Matched related donor HSCT was performed in 29.1% of the patients, matched unrelated donor HSCT in 60.9%, mismatched related in 4% and mismatched unrelated in 6%. Bone marrow (8%), peripheral blood (90%)