The most common fusion partner of JAK2 in BCR-ABL1-like ALL is PAX5; however, the repertoire of fusion partners is still growing as less frequent fusions continue to be discovered.8 In line with this fact, we recently identified a novel JAK2 fusion, NPAT-JAK2, in a patient with BCR-ABL1-like ALL.9 Here we describe this fusion, study its impact on JAK/STAT kinase signaling and its oncogenic potential, and compare it with that of PAX5-JAK2. This evidence concerns the gene PAX5 and acute lymphoblastic leukemia.