Likewise, hypoxia has also been shown to cause G1-phase arrest in p53-deficient prostate carcinoma cells via induction of p21cip1 and p27kip1, but not in p53 wild-type tumor cells such as MCF7 breast cancer cells and RKO colon cancer cells when exposed to ionizing radiation (Graeber et al., 1994; Gardner et al., 2001). Here, TP53 is linked to breast cancer.