We also found that 5-FU-treated RER-positive HCT116 cancer cells (at pHe 7.4) exhibited a dose-dependent increase in phosphorylated ATM, ATR, CHK1, and CHK2, reaching levels observed in untreated acid-exposed cancer cells (pHe 6.5) (Fig. 4E). This evidence concerns the gene CHEK2 and cancer.