PECAM1 and acute myeloid leukemia: The two opposing “faces” of the TKI treatments in FLT3-ITD+ AML models as described here are the initially beneficial cytoreduction of proliferating blasts followed by post-treatment CD31+Sca-1high EC gain and arteriolar re-vascularization of the BM niche that safeguard LSCs thereby creating the condition for disease relapse.