CDKN1A and cancer: The up-regulation of p21(waf1/cip1) and p27(kip1) principally mediate G1 cell cycle arrest, but 1α,25(OH)2D3 has been shown to mediate a G2/M cell cycle arrest in a number of cancer cell lines via direct induction of GADD45A (Akutsu et al., 2001; Jiang et al., 2003; Khanim et al., 2004).