Long-term prognosis for 1-year relapse-free survivors of CD34+ cell-selected allogeneic hematopoietic stem cell transplantation: A landmark analysis

CD34+ cell selection significantly improves GvHD-free survival in allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, specific information regarding long-term prognosis and risk factors for late mortality after CD34+ cell-selected allo-HSCT is lacking. We conducted a single-center landmark analysis in 276 patients alive without relapse 1 year after CD34+ cell-selected allo-HSCT for AML (n=164), ALL (n=33) or myelodysplastic syndrome (n=79). At 5 years' follow-up after the 1-year landmark (range 0.03-13 years), estimated relapse-free survival (RFS) was 73% and overall survival (OS) 76%. The 5-year cumulative incidence of relapse and non-relapse mortality (NRM) were 11% and 16%, respectively. In multivariate analysis, Hematopoietic Cell Transplantation Comorbidity Index score≤3/43 correlated with marginally worse RFS (hazard ratio (HR) 1.78, 95% confidence interval (CI) 0.97-3.28, P=0.06) and significantly worse OS (HR 2.53, 95% CI 1.26-5.08, P=0.004). Despite only 24% of patients with acute GvHD within 1 year, this also significantly correlated with worse RFS and OS, with increasing grades of acute GvHD associating with increasingly poorer survival on multivariate analysis (P<0.0001). Of 63 deaths after the landmark, GvHD accounted for 27% of deaths and was the most common cause of late mortality, followed by relapse and infection. Although prognosis is excellent for patients alive without relapse 1 year after CD34+ cell-selected allo-HSCT, risks of late relapse and NRM persist, particularly due to GvHD.