Conditioning with 8 Gy Total Body Irradiation and Fludarabine for Allogeneic Hematopoietic Stem Cell Transplantation in Acute Myeloid Leukemia: Projected 4-Year Update.

Seventy-one patients with acute myeloid leukemia (AML), most of them (63/71) considered ineligible for conventional allogeneic hematopoietic stem cell transplantation (HSCT), were enrolled into a phase II study on reduced intensity myeloablative conditioning with fractionated 8 Gy total body irradiation (TBI) and fludarabine (120 mg/m²) (Blood. 2005 Nov 1;106(9):3314–21). Patients received mobilized peripheral blood stem cells (n=68) or bone marrow (n=3) from siblings (n=39) or unrelated donors (n=32). HLA-typing was performed for HLA-A, -B, -Cw (serological matching or intermediate resolution DNA typing), DRB1 and DQB1 (high resolution DNA typing). Three patients had unrelated donors with an allele mismatch in HLA DRB1 (2 with an additional mismatch in HLA Cw) and 7 patients were transplanted from unrelated donors with an antigen mismatch in HLA Cw. Thirty-six patients were transplanted in complete remission (CR) and 35 with untreated or refractory disease (non-CR). Median patient age was 51 years (range, 20–66). Sustained engraftment was attained in all evaluable patients. With a median follow-up of now 41.3 months (range, 20.4–70.4) in surviving patients, probabilities of overall survival for patients transplanted in CR and non-CR were 80% (95% CI, 66 to 94%) and 17% (95% CI, 5 – 29%) at 4 years, respectively. Relapse-free survival rates were 57% (95% CI, 39 – 75%) and 14% (95% CI, 2 – 26%). Of the 35 evaluable patients transplanted in CR, 10 patients suffered a relapse between days 68 and 868 after transplantation (cumulative incidence 29%). Five patients with late relapse (>1 year after transplantation) achieved a subsequent CR after conventional chemotherapy, blood stem cell boost and treatment with granulocyte-macrophage colony-stimulating factor, lasting 2000+, 1841+, 909+, 847+ and 480 days, respectively. Depending on donor type, relapse-free survival was similar in patients transplanted from unrelated or sibling donors. Overall survival in patients transplanted in complete remission from unrelated vs. sibling donors was 84% (95% CI, 73 – 95%) vs. 77% (95% CI, 68 – 86%). The cumulative incidence of non-relapse mortality (NRM) in CR patients was 11% at 4 years and beyond (3 patients deceased before day 100 and 1 patient 25 months after transplantation), but amounted to 37% at 4 years in non-CR patients. Nine of the 33 surviving patients (27%) have actually active chronic GvHD (5 limited and 4 extensive disease). This update confirms that allogeneic HSCT from related or unrelated donors with 8 Gy TBI/fludarabine conditioning is feasible with low NRM and preserved long-term antileukemic activity in AML patients in first or later CR.