ERBB2 and breast cancer: In other forms of breast cancer, such as estrogen receptor (ER)- or HER2-positive breast cancer, Notch signaling may initially be lower, but increases in response to endocrine therapies aiming at reducing ER activity or to therapy using HER2-blocking antibodies (trastuzumab) [45,46,47,48,49,50]; for review see [51].