JAK1 and acute lymphoblastic leukemia: It is worth noting that high levels of PIM1 expression are typically found in T-ALL harboring activating mutations of IL7RA, JAK1, JAK3, and STAT5B, and/or loss of function of PTPN2. Accordingly, the highest levels of PIM1 expression have been observed in T-ALL of the TLX1, TLX3, and HOXA subgroups [87,88].