AXL and Patent ductus arteriosus: In proof-of-principle drug screens, the authors find that PDA weanling mice treated for 2 weeks with gemcitabine plus Abraxane and inhibitors of Axl signaling (warfarin or BGB324) have fewer tumor initiation sites and reduced tumor size compared with KIC mice treated with standard-of-care treatments (either gemcitabine alone or gemcitabine plus Abraxane).