Intermediate-dose versus low-dose cyclophosphamide and granulocyte colony-stimulating factor for peripheral blood stem cell mobilization in patients with multiple myeloma treated with novel induction therapies.

Peripheral blood progenitor cell mobilization with intermediate-dose cyclophosphamide (ID-CY) and granulocyte colony-stimulating factor (G-CSF) has been shown to be more efficacious, albeit more toxic, than low-dose cyclophosphamide (LD-CY) mobilization regimens in patients with multiple myeloma treated with conventional therapies. However, the relative importance of cyclophosphamide dose intensity in peripheral blood progenitor cell mobilization after novel induction regimens is not known. Here we report mobilization outcomes of 123 patients who underwent transplantation within 1 year of starting induction chemotherapy with novel agents. We compared consecutive patients undergoing mobilization with ID-CY/G-CSF (3-4 g/m(2)) at one institution (n = 55) with patients receiving LD-CY/G-CSF (1.5 g/m(2)) at a different transplantation center (n = 68). At baseline, the 2 groups were well balanced, except for more frequent previous lenalidomide use in the ID-CY group (P = .04). Compared with LD-CY, ID-CY use was associated with higher median peak PB CD34(+) cell count (35/µL versus 160/µL; P < .001), CD34(+) cell yield on day 1 of collection (2.6 × 10(6)/kg versus 11.7 × 10(6)/kg, P ≤ .001), and total CD34(+) cell yield (7.5 × 10(6)/kg versus 16.6 × 10(6)/kg; P ≤ .001). Six patients in the LD-CY group had mobilization failure, compared with no patients in the ID-CY group. A significantly higher proportion of patients in the LD-CY group (P < .001) were unable to collect ≥5 × 10(6)/kg and ≥10 × 10(6)/kg CD34(+) cells. Neutrophil and platelet engraftment were significantly faster in the ID-CY group, likely because of higher infused CD34(+) cell doses. In conclusion, compared with LD-CY, ID-CY produced a more robust peripheral blood progenitor cell mobilization and significantly reduced the rates of mobilization failure. These data caution against the use of LD-CY-containing mobilization strategies in patients with multiple myeloma undergoing stem cell collection after novel induction regimens.