CHEK2 and malignant colon neoplasm: Intriguingly, the pattern of p53 expression and phosphorylation in mammospheres and monolayer cells bears a resemblance to recent findings with p21-/- and wild type HCT116 colon cancer cells [55], that is high constitutive expression of p53 (and Chk2) and elevated phosphorylation of Ser15 in the untreated p21-/- cells and no change in either expression or phosphorylation in response to oxidative damage induced by chromium.