The stem cell mobilizing capacity of patients with acute myeloid leukemia in complete remission correlates with relapse risk: results of the EORTC-GIMEMA AML-10 trial

Variable numbers of CD34(+) cells can be harvested from the blood of AML patients in CR after G-CSF supported mobilization following consolidation chemotherapy. We hypothesized that a decreased ability to mobilize stem cells reflects a chemotherapy-induced reduction in the number of normal and leukemic stem cells. We therefore analyzed whether the mobilizing capacity of these patients was of prognostic significance. 342 AML-patients in first CR received daily G-CSF from day 20 of the consolidation course and underwent 1-6 aphereses to obtain a minimum dose of 2 x 10(6) CD34(+) cells/kg. Afterwards they were randomized for autologous bone marrow (M) or blood SCT. As a surrogate marker for the mobilizing capacity, the highest yield of CD34(+) cells of a single apheresis was adopted. Patients could be categorized into four groups: no harvest (n = 76), low yield (<1 x 10(6) CD34(+)/kg; n = 50), intermediate yield (1-6.9 x 10(6) CD34(+) cells/kg; n = 128) and high yield ( :7 x 106 CD34+ cells/kg; n = 88). The median follow-up was 3.4 years; 163 relapses and 16 deaths in CR were reported. Autologous blood or BM SCT was performed in 36%, 64%, 81% and 88%, respectively, of the patients assigned to the no harvest, low, intermediate and high CD34(+) yield group. The 3-year disease-free survival rate was 46.7%, 65.0%, 50.4% and 26.9% (P= 0.0002) and the relapse incidence was 47.5%, 30.1%, 43.1% and 71.9% (P < 0.0001). Multivariate Cox's proportional hazards model showed that the CD34(+) yield was the most important independent prognostic variable (P = 0.005) after cytogenetics. Patients with the highest mobilizing capacity have a poor prognosis due to an increased relapse incidence.