Plerixafor Plus Granulocyte Colony-Stimulating Factor versus Placebo Plus Granulocyte Colony-Stimulating Factor for Mobilization of CD34+ Hematopoietic Stem Cells in Patients with Multiple Myeloma and Low Peripheral Blood CD34+ Cell Count: Results of a Subset Analysis of a Randomized Trial

Preapheresis peripheral blood (PB) CD34(+) cell count is a strong predictor of hematopoietic stem cell (HSC) mobilization and is routinely used to optimize the timing, cost, and success of HSC collection in patients with multiple myeloma. However, a uniform PB CD34(+) cell count that predicts mobilization failure has not been defined, resulting in the development of institute-specific algorithms for mobilization, particularly regarding the decision of when to use the novel stem cell mobilization agent plerixafor. In this post hoc analysis, we evaluated the mobilization efficacy of plerixafor plus granulocyte colony-stimulating factor (G-CSF) versus placebo plus G-CSF in patients with multiple myeloma, stratified by preapheresis PB CD34(+) cell count <10, <15, <20, and >= 20 cells/mu L. Regardless of the PB CD34(+) cell count, the total yield of CD34(+) cells from apheresis was significantly higher in the plerixafor group than in the placebo group, and significantly more patients in the plerixafor group collected the minimum (>= 2 x 10(6) cells/kg) and optimum (>= 6 x 10(6) cells/kg) stem cell yields on each day of apheresis. As a corollary, the greater stem cell collection in plerixafor-treated patients resulted in the need for significantly fewer days of apheresis to reach minimum and optimum cell doses across all cell count groups. For all CD34(+) cell count groups, the proportion of patients proceeding to transplantation and the median time to platelet and neutrophil engraftment were similar in the plerixafor and placebo groups. Our findings demonstrate that in patients with multiple myeloma who might be predicted to fail mobilization based on low PB CD34(+) cell count, the addition of plerixafor to G-CSF allows for collection of the minimal and optimal cell doses in a greater proportion of patients compared with G-CSF alone. In addition, plerixafor plus G-CSF significantly improves the likelihood of optimal HSC collection in patients with higher preapheresis PB CD34(+) cell counts (>= 20 cells/mu L) compared with placebo plus G-CSF. Collectively, this analysis of predicted poor mobilizers validates the superiority of plerixafor plus G-CSF compared with G-CSF alone, which had been demonstrated previously in the overall patient population. Biol Blood Marrow Transplant 18: 1564-1572 (2012) (C) 2012 American Society for Blood and Marrow Transplantation