In line with previous findings (Aste-Amézaga et al., 2010), we found differential sensitivity of leukemias to these blockers based on Notch1 mutational status, with Notch1 5′-deletion-harboring tumors being resistant to either mAb, Notch1 PEST-domain mutant tumors being sensitive to both blockers, and tumors characterized by a Notch1 HD-domain mutation exhibiting selective responsiveness to the NRR-targeting antibody. Here, NOTCH1 is linked to leukemia.