The objectives of this study were to identify the predictive factors for the mobilization of CD34 positive peripheral blood stem cells (PBSC) and to determine the optimal timing of PBSC harvest in patients with advanced germ cell tumors after cisplatin-based combination chemotherapy. Thirty-eight patients with advanced germ cell tumors were enrolled in this study. We undertook a retrospective analysis of 124 aphereses performed between March, 1994 and December, 1999. The predictive value for the optimal timing of PBSC harvest was determined by the analysis of the correlation factors between the number of harvested CD34 positive cells and several clinicopathological factors. The mean number of CD34 positive cells obtained at a single apheresis was 5.38x106/kg, and the mean cumulative number of CD34 positive cells in each patient was 24.07x106/kg. The number of CD34 positive cells were significantly correlated to the number of previously performed chemotherapies before PBSC harvest, leukocyte count and the percentage of immature leukocytes (myelocytes plus metamyelocytes) (p=0.0098, p=0.011, and p<0.0001, respectively). Multivariate analysis revealed that the number of chemotherapies and the percentage of immature leukocytes were independent predictors for the number of harvested CD34 positive cells (p=0.012 and p=0.016, respectively). The present findings suggest that PBSC harvest should be performed during first-line chemotherapy, and that the monitoring of the percentage of immature leukocytes could be a useful predictor for determining the optimal timing of PBSC harvest.

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