CDKN1A and cancer: The studies in cancer cells on the effect of vitamin C in regulating p16INK4a and p21 expression seem at odds with the observation in ESCs, iPSCs and tissue specific stem cell cultures in which vitamin C treatment silences the p16INK4a/p19ARF locus and is associated with reduced expression of p53 and p21 (He et al., 2008; Li et al., 2009; Esteban et al., 2010; Li Y. et al., 2016; Zhang P. et al., 2016).