Addition of bortezomib to high-dose cyclophosphamide therapy as a conditioning regimen for autologous peripheral blood stem cell harvest leads to an increased yield of hematopoietic stem cells.

Peripheral blood stem cell harvest (PBSCH) is a crucial procedure for autologous stem cell transplantation in patients with multiple myeloma. We herein report a retrospective study to verify the usefulness of bortezomib and high-dose cyclophosphamide therapy (Bor-HDCY) as a conditioning regimen for PBSCH. Thirty-three patients were evaluated. The median age at the first apheresis was 61 (interquartile range, 53-64) years old, and 18 (54.5%) patients were male. Bor-HDCY was performed in 15 patients, and HDCY was performed in 18. In the patients who underwent Bor-HDCY, the CD34⁺ cell count at the first apheresis was significantly higher than in the others (P<0.01), and the total CD34⁺ cell count also tended to be high (P=0.0933). In terms of apheresis days, two-thirds of the patients who underwent HDCY had two-day apheresis, whereas most who underwent Bor-HDCY had one-day apheresis. According to univariate analysis, Bor-HDCY (P<0.01), VRd (Bor, lenalidomide, and dexamethasone) as induction therapy (P=0.0529), and ≥VGPR before PBSCH (P=0.0767) were factors associated with a higher CD34⁺ cell count at first apheresis. Although multivariate analysis showed that there were no independently significant factors influencing the CD34⁺ cell count at the first apheresis, the stepwise selection method revealed that only the Bor-HDCY regimen remained in the final model (P<0.005). Bor-HDCY may be a useful conditioning regimen for increasing the CD34⁺ cell yield.