Hypothesis : pegfilgrastim at 200 µg/kg between 12 and 18 days after previous chemotherapy provides an efficient stem cell mobilization in children with malignancies Design: phase 2 study. Judgment criterion: percentage of children achieving at least 5x10e6 CD34 cells with a standard apheresis (less than 3 blood volume processed

Patients: consecutively referred for HSC mobilization. 12 to 18 days after the previous chemotherapy. No haematological growth factor during the 8 previous days.

Mobilization: one sc injection of 200 µg/kg pegfilgrastim (Neulasta, Amgen) Evaluation during the study: CD34 circulating cells from day 3 to day 7 ; AE recording Judgment criterion: percentage of children achieving at least 5x10e6 CD34 cells with a standard apheresis (less than 3 blood volume processed) Analysis: sequential Bayesian study

Inclusion Criteria:

• 0 to 18 years
• solid malignancy
• Lansky score >70%
• 12 to 18 days since the beginning of the last chemotherapy cycle
• no administration of any hematopoietic growth factor in the previous 8 days

Exclusion Criteria:

• clinical or biological conditions precluding the mobilization or collection procedure