STAT5 Loss Awakens the Dark Force in Natural Killer Cells.

Natural killer cells (NK) are commonly considered to be potent antitumor effector cells. The study by Gotthardt and colleagues challenges this concept and reveals that STAT5-deficient/inhibited NK cells induce angiogenesis and promote tumor progression. These unexpected findings shed new light on potential adverse effects of JAK-STAT inhibitors in the clinics. ©2016 American Association for Cancer Research.