HIF1A and acute lymphoblastic leukemia: In ACL, hypoxia-inducible factor-1α (HIF-1α) controls Notch1 activity under hypoxia, whereas Notch1ICD is undetectable in non-hypoxic regions of tumors [89], critical findings that are related to what has been observed in T-ALL cells where Notch1 expression and activation, as well as mRNA and protein levels of its downstream target Hes1, are upregulated under hypoxic conditions [90].