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Preceding chemotherapy, tumour load and age influence engraftment in multiple myeloma patients mobilized with granulocyte colony‐stimulating factor alone

Haematopoietic growth factors, especially granulocyte colony‐stimulating factor (G‐CSF), are frequently utilized alone for peripheral blood stem cell (PBSC) procurement to avoid the morbidity associated with high‐dose chemotherapy (HDT). Moreover, the cytotoxic agents used may not be the most optimal therapy for the malignancy. It also makes scheduling of apheresis easier. Factors having an impact on PBSC procurement and engraftment after HDT were analysed in 117 multiple myeloma patients mobilized with G‐CSF (10–16 µg/kg, median 12 µg/kg) alone using Cox regression analysis. A median of 6·2 × 106 CD34 cells/kg (range 0·6–34·1) were procured during leukapheresis and a median of 2·5 × 106 CD34 cells was infused after the first HDT (range 0·3–23·9). The only factor significantly affecting optimal PBSC procurement was duration of preceding conventional chemotherapy (P = 0·002). Granulocyte recovery was prompt in almost all patients, 75% of whom attained a granulocyte count of 0·5 × 109/l by day 13 (median 11, range 7–19). However, platelet recovery to both 20 × 109/l (median 12 d, range 8–50+) and 50 × 109/l (median 20 d, range 7–205+) varied widely. On univariate analysis, factors influencing platelet recovery were the number of CD34 cells/kg infused, age, β2‐microglobulin levels, response to preceding therapy, bone marrow plasmacytosis and duration of prior therapy. Factors attaining significance on multivariate analysis included number of CD34 cells/kg infused (P = 0·007), β2‐microglobulin levels (P = 0·0001), most probably representing disease load, and age (P = 0·002). Patients with high tumour burden, i.e. β2‐microglobulin levels > 2·5 mg/l, probably benefit from chemotherapy for mobilization both in terms of cytoreduction and adequate stem cell mobilization resulting in accelerated engraftment.