A German-Wide Systematic Study on Mobilization and Collection of Hematopoietic Stem Cells in Poor Mobilizer Patients with Multiple Myeloma prior to Autologous Stem Cell Transplantation

Introduction: In patients with a clinical indication for autologous hematopoietic stem cell transplantation (ASCT), sufficient mobilization of CD34⁺ precursor cells into peripheral blood is essential to ensure adequate hematopoietic stem cell (HSC) collection prior to intensive therapy. However, with standard granulocyte-colony stimulating factor (G-CSF)-based mobilization schemes, an important minority of patients fail to mobilize sufficient (e.g., >10/µL) CD34⁺ cell counts into the peripheral blood and are considered as poor mobilizers (PM). Because failure to achieve sufficient CD34⁺ cell mobilization can negatively affect important clinical treatment endpoints, the use of plerixafor (PLX) was approved to increase CD34⁺ mobilization in PM patients. Methods: The German non-interventional, multicenter, open-label, prospective OPTIMOB study evaluated HSC mobilization strategies prior to planned ASCT in adult patients with hematologic malignancies (lymphomas or multiple myeloma [MM]) focusing on PM patients. PM patients were defined as follows: (1) never achieving ≥20 CD34⁺ cells/µL before 1st apheresis, (2) receiving PLX at any timepoint of mobilization, (3) their initially planned stem cell yield had to be reduced, or (4) they had not received apheresis due to low CD34⁺ count in peripheral blood. Results: 168 of 475 MM patients (35%) participating in the OPTIMOB study were classified as PM, and 155 of them (92%) received PLX (PM+PLX) during the study. PM patients were 40–78 years old, slightly more often male (n = 97, 58%), mostly newly diagnosed (n = 146, 87%) and received highly individualized previous treatments. Ninety-four of the PMs underwent chemotherapy mobilization (65%), and 51 patients (35%) received steady-state mobilization with G-CSF only during 1st mobilization attempt. 92% of the total PM population (n = 155) underwent apheresis, 78% of them (n = 117) achieved >2.0 × 10⁶ CD34⁺ cells/kg body weight on the 1st day of apheresis. PM+PLX had a higher median total collection result than those PM patients without PLX support (7.2 vs. 5.7 × 10⁶ CD34⁺ cells/kg body weight). In total, ASCT was performed in 136 PM+PLX (88%) versus 8 PM−PLX patients (62%). Conclusion: The OPTIMOB study showed that a considerable proportion of adult MM patients in Germany are PMs. Even though most of PMs were supported with PLX in the OPTIMOB study, PM-PLX also successfully mobilized HSCs, allowing ASCT in majority of all PMs. However, further analyses are required for treatment optimization in PMs.