Unlike conditional Brca1-null (Brca1co/−/Wapcre/+ and Brca1co/co/Wapcre/+) females, which develop basal-like mammary tumors at a high frequency [26], all conditional-null Ctip animals remained mammary tumor-free over the 24-month observation period (Figure 3C), as did the control animals (n = 10; Ctipco/+/Wapcre/+) (data not shown). Here, BRCA1 is linked to breast cancer.