Ruxolitinib is the first potent, selective, JAK1/2 inhibitor to enter the clinic with IC50 of 3.3 nM/2.8 nM in cell-free assays, >130-fold selectivity for JAK1/2 versus JAK3. Ruxolitinib kills tumor cells through toxic mitophagy. Ruxolitinib induces autophagy and enhances apoptosis.