In the present study, the following two issues were examined: i) The preferred mechanism of cell fate following 5 Gy γ-irradiation, depending on p53 expression in p53 +/+ and p53 −/− HCT116 colon cancer cells; and ii) whether the cell response is p53-associated or p53-independent in HCT116 colon cancer cells. This evidence concerns the gene TP53 and malignant colon neoplasm.