Data on the association of Notch and HER2 expression in breast cancer are quite contradictory since both positive [463,464] and negative [465] relationships between these oncogenes have been reported; however, the interconversion between chemotherapy-sensitive HER2+/Notch1– and GSI-sensitive HER2–/Notch1+ circulating tumor cells underlay the in vivo efficacy of simultaneous treatment with GSI LY-411575 or RO4229097 and paclitaxel [466]. Here, NOTCH1 is linked to breast cancer.