Peripheral blood stem cell mobilisation with G-CSF alone versus G-CSF and cyclophosphamide after bortezomib, cyclophosphamide and dexamethasone induction in multiple myeloma

Bortezomib-based induction is often used in transplant-eligible patients with myeloma. The optimal peripheral blood stem cell (PBSC) mobilisation strategy in this context is unclear. We reviewed the efficacy of G-CSF alone (G-alone) vs. G-CSF and cyclophosphamide (G-cyclo: standard dose: 1.5-2 g/m²; high dose: 3-4 g/m²) PBSC mobilisation strategies in 288 patients who only received bortezomib, cyclophosphamide and dexamethasone (VCD) induction prior to autograft across six apheresis centres from November 2012 to June 2017. 'Uncomplicated successful mobilisation' was defined as achieving a PBSC yield of ≥4 × 10⁶/kg within two aphereses, without plerixafor or mobilisation-associated toxicity (predominantly febrile neutropenia, FN). Success rates were 84% in G-cyclo standard dose (6% FN), 64% in G-cyclo high dose (18% FN) and 69% in G-alone (plerixafor successfully salvaged 8/9 patients). Median total stem cell yield was significantly higher with G-cyclo, but not different between the two cyclophosphamide doses. Age greater than the median of 61 years was associated with higher failure rates (22 vs. 11%, p = 0.01) and lower PBSC yield, especially in the G-alone group. Prior radiotherapy exposure did not impact on collection success. Our observations suggest that both G-cyclo standard dose and G-alone are reasonable mobilisation strategies. The former may be preferred if salvage plerixafor is unavailable.