Factors influencing mobilization and engraftment of PBSC were analyzed in 38 patients with metastatic breast cancer who were undergoing PBSC transplantation. None of these patients had had previous chemotherapy for metastatic disease. PBSC were mobilized with cyclophosphamide (CY) and G-CSF (n = 21) or CY and etoposide (CY-etoposide) and G-CSF (n = 17). All received cyclophosphamide 6000 mg/m2, thiotepa 500 mg/m2, and carboplatin 800 mg/m2 (CTCb) as preparative regimen. PBSC infusion was followed by G-CSF at 5 μg/kg in 30 patients or 10 μg/kg in 8 patients. A median number of 27 x 106 CD34+ cells/kg was obtained with a median of four aphereses. Previous chemotherapy, radiation therapy, marrow disease, time from previous chemotherapy to mobilization, and type of mobilization regimen did not have a statistically significant effect on collection efficiency (CE). CE was defined as the total number of CD34+ collected/number of collections. Engraftment was rapid, with patients reaching a neutrophil count of 0.5 x 109/L a median of 9 days (range 7-23) and a platelet count of 20 x 109/L a median of 12 days (range 8-28) after transplantation. Shorter times to platelet recovery were associated with a higher number of CD34+ cells infused (p = 0.012), CY mobilization (p = 0.033), and a lower number of prior chemotherapy cycles (p = 0.022). When the number of CD34+ cells was included in the proportional hazard model, no other variables were found to be significant predictors of platelet engraftment. Time to neutrophil recovery was negatively associated with the dose of G-CSF used after transplantation (p = 0.036) CD34 cell dose is an important predictor of engraftment kinetics. A posttransplant dose of G-CSF improves neutrophil recovery. For patients with metastatic breast cancer and no previous chemotherapy for metastatic disease, we have no evidence for a difference between CY and CY-Etoposide as the mobilization regimen.
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