This is the first Tunisian study in which we report the incidence of t(12;21) among childhood B-lineage ALL and in which we have found multiple copies of RUNX1.Finally, our findings confirm that additional or secondary genetic changes are commonly encountered in pediatric B-lineage ALL with ETV6-RUNX1 gene fusion which is envisaged to play a pivotal role in disease progression. Here, ETV6 is linked to acute lymphoblastic leukemia.