Increment of hematopoietic progenitor cell count as an indicator of efficient autologs stem cell harvest in patients with multiple myeloma.

We previously showed that hematopoietic progenitor cell (HPC) count is a useful surrogate for the timing of autologs stem cell collection (ASCC). We investigated the role of HPC count increment in predicting the time for optimal ASCC in patients with multiple myeloma (MM). Between May 2002 and January 2011, 138 patients with MM who underwent ASCC after mobilization with cyclophosphamide (4 g/m(2)) and granulocyte-colony stimulating factor at Asan Medical Center. HPC monitoring was started on the 10th day of cyclophosphamide administration and ASCC was performed when HPC count reached at least 10/mm(3). Velocity of HPC increment (/mm(3) /day) was calculated as HPC count on the first day of ASCC/number of days from cyclophosphamide infusion to the first day of ASCC. A total of 422 leukapheresis were performed in 136 patients (median per patient: 3; range: 2-8). Of these patients, 131 (94.9%) successfully achieved optimal ASCC (≥5 × 106 CD34+ cells/kg). The median velocity of HPC increment was 2.17/mm(3) /day (range: 0.07-144.2/mm(3) /day). The mean ± standard error numbers of apheresis procedures in patients with velocity of HPC increment ≤2.0/mm(3) /day and >2.0/mm(3) /day were 3.43 ± 0.17 and 2.70 ± 0.11, respectively, and their median times to optimal ASCC were 15 and 13 days, respectively, with a hazard ratio of 0.47 (95% confidence interval, 0.32-0.68; P < 0.001) on multivariate analysis. Therefore, a slower increase of HPC of ≤2.0/mm(3) /day is associated with larger number of apheresis procedures for optimal ASCC.