Fractionated High-Dose Cyclophosphamide and G-CSF: An Extremely Effective Chemo-Mobilization Modality In Patients With Multiple Myeloma

The optimal stem cell mobilization regimen for multiple myeloma (MM) is undefined. Most centers use either granulocyte-colony stimulating factor (G-CSF) alone (steady state strategy) or cyclophosphamide (CY) followed by G-CSF (chemo-mobilizing strategy). However, the impact of CY dose on stem cell yield and subsequent engraftment, and toxicity is unknown. We retrospectively analyzed our experience using fractionated high-dose CY and G-CSF as our preferred chemo-mobilization strategy in MM patients (pts) and its impact on the mobilization outcomes, engraftment and the observed toxicity.

Between 01/2000 and 12/2012, 220 chemo-mobilization attempts were undertaken. Among these, 62 pts (M=37, F=25) had MM (1^st-line=54, relapsed=8) and all received high-dose CY and G-CSF. Median age was 56 (37-75) yrs. ISS stage was I (n=34), II (n=16), and III (n=12). Pre-transplant induction consisted of VAD or VAD-like chemotherapy (n=26), bortezomib(bor)/dexamethasone (dex) (n=15), thalidomide (thal) /dex (n=10), bor/thal/dex (n=10), and 1 received bor/lenalidomide/dex. Fifty-six received fractionated high-dose CY (5g/m² divided in 5 doses of 1g/m² q 3 hrs) whereas 6 received CY 50 mg/kg for 2 doses. G-CSF was given at a fixed dose of 300 µg SQ q 12 hrs.

All 62 (100%) pts achieved a circulating CD34 count ≥20/µl which is the cut-off level at our center to proceed with apheresis. The median peak peripheral blood CD34+ cell count was 111.5 (21-575) cells/μL. Success rate of stem-cell mobilization defined as collection of more than 2x10⁶ CD34+ cells/kg was 100%. Median stem cell collection yield was 15.9x10⁶ CD34+ cells/kg. Moreover, 61 (98.4%) pts and 46 (74%) pts collected >5x10⁶ and >10x10⁶ CD34⁺ cells/kg, respectively. Only 4 (6.4%) pts required 2 apheresis sessions. Conversely, 40 (64.5%) pts required hospitalization for febrile neutropenia (n=38) or transfusion support (n=2) for a median of 4 (1-8) days. No one required intensive level of care and all recovered. Also, 17 (27.4%) pts required blood transfusions and 16 (25.8%) required platelets transfusion. Autografting was successfully performed in all pts using high-dose melphalan with a median time from mobilization to the first transplant of 31 (16-156) days and median infused CD34+ cells of 7x10⁶/kg (3.1-15.3). All pts achieved successful hematologic engraftment with a median time for neutrophil engraftment (ANC ≥500/µL) of 11 days and platelet engraftment (platelet ≥20000/microliter) of 12 days.

Fractionated high-dose CY and G-CSF is a highly effective chemo-mobilization strategy in MM in terms of successful rate of mobilization (100%), efficiency of stem cell collection (high yield), and timely hematologic engraftment (100%). However, the relatively high-rate of hospitalizations for febrile neutropenia requires an assessment of its cost-efficiency as compared to new mobilization strategies using G-CSF and preemptive plerixafor.

No relevant conflicts of interest to declare.