Tumors for which inhibition of Notch signaling may be particularly desirable include breast cancer, where high levels of Notch1 signaling are associated with poorer prognosis [28], [31], and T-ALL, in which activating mutations in Notch1 are found frequently and where treatment with Notch pathway inhibitors, such as GSIs, arrests growth [34], [40], [41]. This evidence concerns the gene NOTCH1 and breast cancer.