PB2357 HAPLOIDENTICAL TRANSPLANTATION IN PATIENTS WITH HIGH‐RISK OR RELAPSED/REFRACTORY (R/R) ACUTE MYELOID LEUKEMIA: 3 YEARS EXPERIENCE OF ONE CENTER

Background: Allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is the potentially curative option for patients with high‐risk acute myeloid leukemia or in the case of R/R disease. However, a number of patients with indications for performing allo‐HSCT do not have HLA‐ identical related or unrelated donor, or the search for a donor is associated with a long time, and the expected duration of remission is short. We evaluated clinical outcomes of haplo‐HSCT in patients with high‐risk or R/R AML. Aims: To evaluated clinical outcomes of haplo‐HSCT in patients with high‐risk AML or R/R disease. Methods: 34 patients with high‐risk or R/R AML who had undergone haplo‐HSCT in our center between December 2015 and December 2018 were included, and data were retrospectively analyzed. All patients received reduced intensity conditioning (RIC) regimen. Posttransplantation cyclophosphamide (50 mg/kg Day + 3, +4), tacrolimus and mycophenolate mofetil was administered to prevent graft‐versus‐host disease (GVHD). Stem cell sources was granulocyte colony‐stimulating factor‐primed bone marrow – 8% (median CD34 ‐ positive cells ‐ 3.9∗10 6 /kg) and peripheral hematopoietic stem cells – 92% (median CD34 ‐ positive cells – 5.92∗10 6 /kg). The median age of patients who underwent allo‐HSCT was 39 years (range, 21‐66). Chemoresistant disease at transplantation had 11 patients (32.3%). A high risk group for AML was determined using cytogenetic risk stratification in 39% of patients (complex or monosomal karyotype, FLT‐ITD and c‐KIT mutation), 61% based on clinical data (no remission after two courses induction therapy or early relapse AML). Results: Over a median follow‐up of 16.5 months (1‐35.9 months), 24 out of the 34 patients (70%) were alive. Overall survival (OS) and progression free survival (PFS) rate at 1‐years was 64.5% and 61.7%. With a median follow‐up of 16.5 months the median OS was not reached in patients who received allo‐HSCT in remission; in the group of R/R AML median OS was 4.13 months. 1‐years OS was significantly higher in the group of patients who achieved remission at the time of allo‐HSCT: 79.3% and 40.4% (p = 0.012). 1‐years PFS was 74.8 % and 36.4 % respectively (p = 0.005). In the group with R/R AML, 50% of relapses after allo‐HSCT developed during the first 89 days. The incidence of acute GVHD grade 1‐4 was 28.2%; grade 3‐4 ‐ 14.5%. The incidence of chronic GVHD was 32.7%; severe cGVHD ‐ 16.9%. For the prevention of relapse after allo‐HSCT, 18 pts. (53%) received therapy with hypomethylating agents (azacytidine and decitabine), 5 patients (14.7%) received preventive donor lymphocytes infusion. Summary/Conclusion: Haploidentical hematopoietic stem cell transplantation is an effective and safe therapeutic option in patients with high‐risk AML. However, the results of treatment of patients with R/R AML remain poor. Achieving remission at the time of allo‐HSCT with the use of new drugs will be associated with improved therapy for these patients.