Center Characteristics and Procedure-Related Factors Have an Impact on Outcomes of Allogeneic Transplantation for Patients with CLL: A Retrospective Analysis from the European Society for Blood and Marrow Transplantation (EBMT)

Introduction:Even in the era of novel targeted therapies for the treatment of Chronic Lymphocytic Leukemia (CLL) patients, such as BTK, PI3K and BCL2 inhibitors, allogeneic hematopoietic stem cell transplantations (alloHCT) will remain an important treatment option for a subset of patients with very high risk CLL. The current study focused on the impact of center and procedure-related factors on outcomes after alloHCT, taking into account the impact of patient- and disease-related risk factors. Patients and Methods:Data of 684 CLL patients who received a first alloHCT between 2000 and 2011 were analyzed. Their data were collected as part of the EBMT CLL Data Quality Initiative. Outcomes of interest were Event-Free Survival (EFS) up to 5 years after transplantation and mortality in the first 100 days after alloHCT. Outcomes were analyzed by means of the Kaplan-Meier method and Cox proportional hazards models with a frailty (random effects) component to take into account unexplained center heterogeneity. The following factors describing center characteristics or the transplant procedure were analyzed: experience in alloHCT in general and, for CLL specifically, accreditation by the Joint Accreditation Committee-ISCT & EBMT (JACIE), Gross National Income (GNI)/capita based on purchasing power parity (PPP) (GNI/cap), donor type, donor-patient sex-match, type of conditioning, stem cell source and T-cell depletion (TCD). Results:Five-year EFS of the whole cohort was 37% (95% Confidence Interval, 33%-42%), Day-100 survival was 90% (88%-92%). Experience of the transplant center was measured by the number of all alloHCTs, and alloHCTs for patients with CLL respectively. The median total number of alloHCTs per center per year was 45 (range 0-169) and the median number of CLL alloHCTs was only 2 per center per year (range 0-19). Greater experience with transplantation of patients with CLL (Hazard Ratio (HR) 0.96 per additional transplant, p=0.002), JACIE accreditation (HR 0.7, p=0.045) and a higher GNI/cap (HR 0.4, 95% CI 0.2-0.96, p=0.04) showed a protective impact on 5-year EFS in the Cox model. In vivo TCD with alemtuzumab (HR 1.5 compared to no TCD, p=0.03) and a female donor for a male patient (HR 1.4 compared to a male donor for a male patient, p=0.02) were the only procedure-related factors significantly associated with EFS. Event-Free Survival after in vivo TCD with Anti-Thymocyte-Globulin or after ex vivo TCD was comparable to EFS without TCD (HR 0.9, 0.7-1.3