From 1 January 2015 to 31 December 2020, thirty-nine patients, 0–21 years old with r/r BCP-ALL were treated with blinatumomab with the aim of inducing remission (n = 13) or reducing MRD levels (n = 26) in the frame of different multiagent chemotherapy schedules, in seven AIEOP centers. This evidence concerns the gene OPN1SW and acute lymphoblastic leukemia.