Allogeneic Blood or Marrow Transplantation with High-Dose Post-transplantation Cyclophosphamide for Acute Lymphoblastic Leukemia in Patients Aged ≥55

Patients ≥55 years-old with acute lymphoblastic leukemia (ALL) fare poorly with conventional chemotherapy with 5-year overall survival of ∼20%. Tyrosine kinase inhibitors and novel B-cell targeted therapies improve outcomes, but rates of relapse and death in remission remain high. Allogeneic blood or marrow transplantation (AlloBMT) provides an alternative consolidation strategy, and post-transplantation cyclophosphamide (PTCy) facilitates HLA-mismatched transplants with low rates of non-relapse mortality (NRM) and graft-versus-host disease (GVHD).The transplant database at Johns Hopkins was queried for patients ≥ 55 years old who received alloBMT for ALL using PTCy.The database included 77 such patients. Most received reduced-intensity conditioning (RIC) (88.3%), were in first remission (CR1) (85.7%), and had B-lineage disease (90.9%). For the entire cohort, 5-year relapse-free survival (RFS) and overall survival (OS) were 46% (95% CI 34-57) and 49% (95% CI 37-60). Grade 3-4 acute GVHD occurred in only 3% of patients and chronic GVHD in 13%. In multivariable analysis, myeloablative conditioning led to worse RFS (HR 4.65, p=0.001); while transplant in CR1 (HR 0.30, p=0.004), and transplant for Ph+ ALL vs. T ALL (HR 0.29, p=0.03) improved RFS. Of the 54 patients who received RIC alloBMT in CR1 for B ALL, 5-year RFS and OS were 62% (95% CI 47-74) and 65% (95% CI 51-77), respectively, with a 5-year relapse incidence of 16% (95% CI 7-27) and NRM of 24% (95% CI 13-36).RIC AlloBMT with PTCy in CR1 represents a promising consolidation strategy for B ALL patients ≥ 55 years old.NIH grants P01 CA225618 and P30 CA06973.