STAT3 and acute lymphoblastic leukemia: With respect to T-ALL development, two pathogenetic links have been described to date: (a) the signaling axis involving miR-21 and PDCD4 in Notch-mediated induction of T-ALL and (b) miR-21-mediated STAT3 inhibition, prompting increased proliferation and invasion and diminishing the apoptosis rate [179,180].