To identify somatically acquired second hits leading to B-ALL development in Pdcd1fl/fl;Mb1-Cre;Pax5+/− mice, we performed whole-genome sequencing of paired tumor and germline samples from two Pdcd1fl/fl;Mb1-Cre;Pax5+/− tumors. This evidence concerns the gene PAX5 and precursor B-cell acute lymphoblastic leukemia.