Despite advances in their classification and treatment, acute leukemia remain incurable disease for the majority of patients. It is necessary to identify new prognostic markers of survival and new therapeutic targets to improve prognosis. Some studies have shown that Fms-like tyrosine kinase 3-ligand (FLT3-L) could be interesting from this. A more recent study from our group testing a novel therapy in acute lymphoblastic leukemia, showed an increase of this marker in the blood of patients responding to treatment. The aim of our prospective, non-interventional study is to measure the plasma levels of FLT3-L at different times of the management of patients with acute lymphoblastic leukemia but also myeloid. For this, analyzes of the samples collected in the usual care will be conducted to study the relationship between the plasma concentration of FLT3-L and outcomes. If there is any link, the FLT3-L could serve as a predictor of treatment response.