Although Notch-2 has a dual role as a tumor suppressor or oncogene in breast cancer (reviewed in [62]), a recent study showed that treatment of patient-derived xenografts of epithelial tumors including breast with the Notch-2/Notch-3 antagonist tarextumab suppressed tumor growth and reduced tumor-initiating cell frequency [39]. This evidence concerns the gene NOTCH3 and breast carcinoma.