Introduction: Poor engraftment represents one of the possible complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It presents as pancytopenia or bicytopenia, with or without complete donor chimerism. There are three entities of poor engraftment: poor graft function (PGF), graft failure (GF), and graft rejection (GR). Aim: This study aims to show the frequency of poor engraftment, as well as the frequency of all of its entities individually, among the patients of the Clinic of Hematology of the University Clinical Center of Serbia (UCCS), who underwent allo-HSCT between December 20, 2017 and December 25, 2020, for the purpose of achieving improved management and understanding of this serious complication. Materials and methods: This retrospective cohort study included 58 patients. Diagnosis of poor engraftment was confirmed by pancytopenia (cut off values: hemoglobin < 70g/L; platelet count < 20 x 109 /L; absolute neutrophil count (ANC) < 0.5 x 109 /L), for three consecutive days, as of day D+28, with the exclusion of severe graft versus host disease (GvHD) and relapse, with complete donor chimerism in PGF and with incomplete donor chimerism in GF. GR presented as acute rejection of the graft by the recipient with bone marrow aplasia or pancytopenia. Results: Poor engraftment was confirmed in 13 of 58 patients (22.4%). Patients with PGF were the majority, with 12.1% (seven patients), while patients with GF and those with GR had the same incidence of 5.2% (three patients). Overall survival for patients with poor engraftment after allo-HSCT was five months, which is significantly less than the overall survival of the patients who had good engraftment after allo-HSCT (57 months). Conclusion: The three types of poor engraftment must be precisely discriminated and diagnosed in relation to donor chimerism in order to decrease morbidity and mortality in patients, post allo-HSCT.

Introduction/Aim: Disease relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is one of the most common and most severe post transplantation complications and represents the leading cause of treatment failure and patient death. The aim of this study is to assess the frequency and types of relapse, in relation to the time of occurrence; analyze the influence of conditioning regimens on relapse occurrence; review the therapeutic options after the occurrence of relapse; assess the prognosis in patients with relapse. Methods: This retrospective cohort study included 58 patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). Pre-transplantation therapy was performed with a reduced-intensity conditioning regimen (RIC) or a myeloablative regimen (MAC). The diagnosis of relapse was made through myelogram analysis, analysis of cytogenetics, analysis of minimal residual disease (MRD), analysis of cellular chimerism, and analysis of immunohematological chimerism of blood group antigens. A database was formed in relation to the examined patient characteristics. Patient survival was analyzed using the Kaplan-Meier method and the log-rang test. Results: MAC (43 patients) was used more frequently than RIC (15 patients), as a conditioning regimen. After transplantation, 18 (34%) out of 53 patients had a relapse. The choice of regimen did not affect the occurrence of relapse, but patients on the RIC regimen lived longer (38.5 ± 7 months) as compared to patients on the MAC regimen (27.8 ± 3.5 months). However, the difference in survival was without statistical significance (p = 0.318). The median survival time of patients who relapsed was 26 ± 5 months, while patients without disease relapse had a median survival time of 41 ± 4 months. Conclusion: Patients who received reduced-intensity regimens (RIC) had a longer survival time, without an increase in the relapse rate. In future, consideration should be given to the inclusion of patients older than 60 years, as candidates for transplantation, as well as to the possible use of prophylactic therapy aimed at preventing relapse in high-risk patients.