High CUL4A expression was associated with reduced sensitivity to gemcitabine in lung cancer cells and to cisplatin in colorectal cancer cells.[21,22] Overexpression of CUL4A in normal mammary epithelial cell line MCF10A abrogated the G2/M cell cycle checkpoint and prevented p53 accumulation in response to DNA damage induced by ionizing irradiation, thus contributing tumorigenesis and/or tumor progression.[23] The role of CUL4A in resistance to chemotherapy and radiotherapy can be explained by its regulation on proteolysis of p53. This evidence concerns the gene TP53 and colorectal cancer.