In this respect, since Notch4 was suggested to be relevant in regulating the basal breast SC population, while Notch1 function could be more likely confined to luminal precursors both in the normal mammary gland as well as in breast cancer (Dontu et al, 2004; Bouras et al, 2008; Raouf et al, 2008; Harrison et al, 2010), our findings now would place Pin1 as a key regulator of stage-specific physiologic and pathologic Notch functions in this epithelial compartment. This evidence concerns the gene NOTCH4 and breast cancer.