Poor Peripheral Blood Stem Cell Mobilization Correlates with Worse Long-Term Outcomes in Multiple Myeloma Patients Undergoing Autologous Stem Cell Transplantation

Introduction: Poor peripheral blood stem cell (PBSC) mobilization has been shown to be associated with worse outcomes in lymphoma patients undergoing autologous stem cell transplantation (ASCT). The impact of poor mobilization on the outcome of ASCT in multiple myeloma (MM) patients has not been well studied. In this single institution retrospective study, we evaluated the effect of poor mobilization on PFS and OS for MM patients undergoing ASCT. Methods: We collected data retrospectively for patients with MM who underwent ASCT between Jan. 2001 and Dec. 2010.  Patients were initially mobilized with standard-dose (10 mcg/kg/day) granulocyte colony stimulating factor.  Patients were classified as poor mobilizers if they failed to collect > 4×10⁶ CD34+ cells/kg from all apheresis attempts. The log-rank test was used to analyze PFS (from ASCT to first relapse) and OS (from diagnosis to death) for both groups. Multivariate analysis by the Cox proportional hazards model was used to assess the correlation of mobilization with other known prognostic variables and PFS and OS. Results: Total of 271 patients were identified for study inclusion.  Of these, 13 patients were excluded due to loss of follow-up beyond 6 months (8), progressive disease through ASCT (3), development of second malignancies (2).  The mean length of follow-up for all patients was 74.5 months.  Thirty-seven (14.3%) patients were poor mobilizers and 221 (85.7%) were good mobilizers. Univariate analysis showed no significant difference between the two groups in regards to age, gender, beta-2 microglobulin (B2M) level at diagnosis, and disease status at time of ASCT, but there was significant differences in disease stage at presentation (86.5% had Durie-Salmon disease stage 3A or 3B vs. 63.8%, p = 0.007), number of prior chemotherapy regimens (67.6% had ≥ 2 prior regimens vs. 43.8%, p = 0.005), and ideal body weight (median 67.2 vs. 62.3 kg, p = 0.015) in poor vs. good mobilizers, respectively. Survival analysis for poor versus good mobilizers showed a median PFS of 24.7 months vs. 28.7 months (p = 0.08) and median OS of 52.8 months vs. 106.8 months (p < 0.0001), respectively. Cox PH regression multivariate analysis showed significant correlation of PFS to disease stage and number of prior chemotherapy regimens, while B2M and number of prior chemotherapy regimens correlated significantly to OS. However, poor mobilization was not significantly correlated to PFS (p = 0.963) or OS (p = 0.087). After ASCT, good mobilizers were more likely to be in VGPR/CR than poor mobilizers (53.4 vs. 37.8%, respectively). Conclusions: Poor PBSC mobilization is associated with worse long-term outcomes in MM patients undergoing ASCT. Our data suggests that poor mobilization was not independent predictive factor, possibly due to small number of patients, but significantly associated with a more advanced disease stage and ≥ 2 of pre-transplant chemotherapy regimens.