Although all activating NOTCH1 mutations confer constitutive and/or prolonged NOTCH1 signaling, only some of them, such as those leading to constitutive expression of the NICD form of NOTCH1, promote “strong” NOTCH1 signaling and have the intrinsic capacity to induce T-ALL in murine models [19]. Here, NOTCH1 is linked to acute lymphoblastic leukemia.