In summary, this study consisted of two parts: (1) the identification of TEL/AML1 + HSPC subpopulation representing the parental cell of origin of TEL/AML1 + ALL; (2) the monitoring of genetic instability in genes often associated with ALL (TEL, AML1, BCR, ABL, MLL) and their PFG. This evidence concerns the gene BCR and acute lymphoblastic leukemia.