Achieving stringent CR is essential before reduced-intensity conditioning allogeneic hematopoietic cell transplantation in AML.

Reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (allo-HCT) can cure patients with AML in CR. However, relapse after RIC allo-HCT may indicate heterogeneity in the stringency of CR. Strict definition of CR requires no evidence of leukemia by both morphologic and flow cytometric criteria. We re-evaluated 85 AML patients receiving RIC allo-HCT in CR to test if a strict definition of CR had direct implications for the outcome. These patients had leukemia immunophenotype documented at diagnosis and analyzed at allo-HCT. Eight (9.4%) had persistent leukemia by flow cytometric criteria at allo-HCT. The patients with immunophenotypic persistent leukemia had a significantly increased relapse (hazard ratio (HR): 3.7; 95% confidence interval (CI): 1.3-10.3, P=0.01) and decreased survival (HR: 2.9; 95% CI: 1.3-6.4, P<0.01) versus 77 patients in CR by both morphology and flow cytometry. However, the pre-allo-HCT bone marrow (BM) blast count (that is, 0-4%) was not significantly associated with risks of relapse or survival. These data indicate the presence of leukemic cells, but not the BM blast count affects survival. A strict morphologic and clinical lab flow cytometric definition of CR predicts outcomes after RIC allo-HCT, and therefore is critical to achieve at transplantation.