CD19 and acute lymphoblastic leukemia: Our study demonstrates that blinatumomab is effective in inducing complete remission in children with R/R CD19+ pre-B ALL, with 75% of patients achieving remission after a single cycle, and 73.3% after two cycles, although the difference between the groups was not significant, this could be due to the fact that patients with a greater number of lines of prior chemotherapy treatment and older > 10 years of age were concentrated in the group that received 2 cycles, only 2 patients who had achieved a partial response with the first cycle achieved a complete remission with the 2nd cycle.