In an experiment involving the transplantation of wild-type (wt)-p53 or p53-null HCT116 human colon cancer cells into athymic female nude mice, after 20 Gy electron irradiation of the local tumor, non-irradiated wt-p53 distant tumors exhibited significant inhibition of tumor growth, whereas p53-null tumors did not show a noticeable difference. This evidence concerns the gene TP53 and malignant colon neoplasm.