On-Demand Plerixafor with Cyclophosphamide and G-CSF for Hematopoietic Stem-Cell Mobilization in Multiple Myeloma Patients: Preliminary Results of a Prospective Observational Study (MOZOBL06877)

Background. High-dose melphalan followed by autologous stem cell transplantation is a standard of care in transplant-eligible newly diagnosed multiple myeloma (NDMM) patients and is also an option at relapse. Therefore, since the minimum number of CD34+ cells required to ensure adequate bone marrow recovery after myeloablative chemotherapy is 2x10^6/kg, an adequate upfront stem-cell collection is necessary in MM patients. Approximately 5-15% of MM patients mobilized with granulocyte colony-stimulating factor (G-CSF) or G-CSF+cyclophosphamide (G-CSF/CY) fail stem-cell collection (<2x10^6/kg CD34+). Plerixafor in combination with G-CSF or G-CSF/CY increases stem-cell yield and lowers the rate of poor mobilizers (PM). Here we present preliminary results of the prospective, observational MOZOBL06877 study (partially supported by Sanofi investigation funds) to evaluate the performance of stem-cell mobilization with G-CSF/CY plus on-demand plerixafor in NDMM patients treated with novel agents.

Methods. NDMM patients undergoing stem-cell mobilization with cyclophosphamide (2-4 g/m²) and G-CSF (5-10 mcg/kg/day), with on-demand plerixafor according to clinical practice (<20 CD34+/ul on first count day or <1×10⁶ CD34⁺ cells/kg collected on first apheresis day), could be enrolled and were observed for 30 days after mobilization. The primary endpoint was the PM rate (patients collecting <2×10⁶ CD34⁺ cells/kg); secondary endpoints were the number of patients requiring plerixafor, the stem-cell yields with or without plerixafor, the identification of predictive factors for the use of plerixafor and adverse events (AEs) during study treatment.

Results. At the data cut-off (09 June 2020), a total of 252 patients had been enrolled: of these, 192 patients (59, 29-72 years) were available for the analysis. The median number of induction cycles before mobilization was 4 (range 1-7); median time from diagnosis to mobilization was 6 months (IQR 5-8). Induction therapy consisted of a bortezomib-based regimen in 171 (90%), carfilzomib/lenalidomide-based regimen in 14 (7%), lenalidomide-based regimen in 3 patients (2%). 187/192 (97%) patients successfully collected ≥2 x 10^6/Kg CD34: of these, 153/192 (80%) collected with G-CSF/CY, 29/192 (15%) required the administration of plerixafor. The PM rate was 5/192 (2.5%): of these, 3/5 did not receive plerixafor in addition to G-CSF/CY, while 2/5 failed stem-cell collection despite the use of plerixafor. The median number of CD34 collected was 9.8x10^6/Kg (6.7-14.2). The median number of CD34/Kg collected with or without plerixafor was 5.1 (4.3-9.1) and 10.6 (8.1-14.4), respectively. The median number of apheresis days was 1 (IQR 1-2), with a stem-cell collection efficiency (CD34 number collected/ days of apheresis) equal to 7.7 x10^6 CD34/kg/day. The median number of apheresis days was 1 without plerixafor and 2 with plerixafor, with a stem-cell collection efficiency (CD34 number collected/ days of apheresis) equal to 8.8 without plerixafor and 3 with plerixafor. In patients who received plerixafor, the median number of CD34/ul pre-apheresis was 16 (10-19.5); after the administration of plerixafor, the median number of CD34/ul pre-apheresis increased to 46 (21-81). Non hematological AEs within 30 days after mobilization occurred in 8% of patients (grade 3-4: 2%); all grade and grade 3-4 infections occurred in 2% of patients each. In a multivariate analysis, main factors predicting the use of plerixafor were ISS 3 (vs. 1, OR 4.43; p=0.008), bone marrow plasma cells at diagnosis >60% (OR 3.85; p=0.006), white blood cell (WBC) count pre-mobilization (OR 6.66; p<0.001) and lenalidomide-based therapy (OR 3.85; p=0.03).

Conclusion. "On-demand" plerixafor combined with G-CSF/CY is a safe and effective rescue strategy for stem-cell collection in MM, reducing the PM rate to 2.5%. Extensive bone marrow plasmacytosis, ISS 3 disease at diagnosis, use of lenalidomide during induction and a low WBC count pre-mobilization predicted the use of plerixafor. Thus, pre-emptive administration of plerixafor in patients presenting one or more risk factors for poor mobilization might help in further reducing the PM rate.

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