Moreover, an activating Jak1 p.F837V variant was identified in one of the leukemic samples, which again highlights the importance of the JAK/STAT-signaling pathway in Pax5+/− leukemias, as shown for Jak1 and Jak3 mutations in the Pax5+/− delayed-exposure B-ALL3,25. Here, PAX5 is linked to leukemia.