The p53 gene and protein in 2005: new results, promising opportunities. The p53 gene is one of the most important genes which is involved in the regulation of cell division and tumor formation. The normal function of the p53 protein is to arrest the cell division and to turn the cell towards apoptosis in the case of cell stress and DNA damage, thereby to protect the integrity of the genome. Several p53 gene mutations that have function in carcinogenesis have been found in various tumors, including gastrointestinal carcinomas. The loss of p53 response plays an important role in the malignantly transformed cell proliferation. Promising experiments try to substitute the lost functions of the p53 gene. With their help new anti-tumor therapeutic methods should be developed.