P53 mutations are common in colorectal cancer. Immunohistological staining of primary colorectal carcinomas with p53-specific antibodies showed p53 overexpression in about 50% of malignant tumors, while benign adenomas were negative. Analysis of 10 colorectal cancer cell lines revealed that six expressed high levels of p53, which were found to be mutant. In two of these four cell lines with lower p53 expression, point mutations were still detected. This indicates that p53 overexpression is synonymous with mutation, but some mutations may not be detected by simple immunohistochemical analysis. Mutation of the p53 gene is one of the most common genetic changes in colorectal cancer. Understanding the genetics and biology of colorectal cancer is crucial for developing new prevention and treatment strategies. The p53 gene, located on chromosome 17p, is a key genetic change in colorectal cancer. Mutations in the p53 gene are found in a high proportion of lung, breast, and other tumors. Studies show that many human tumor-derived cell lines express elevated levels of p53, which can be explained by mutated forms of p53 that stabilize the protein. Immunohistochemical studies with monoclonal antibodies to p53 showed that a high proportion of colorectal carcinomas stained with these antibodies, while normal colonic epithelium was uniformly negative. Analysis of p53 protein expression in 10 colorectal cancer-derived cell lines showed that six expressed high levels of p53, which were found to be mutant. The remaining four cell lines did not express detectable levels of p53 protein, but all contained p53 mRNA. Direct sequencing and chemical-mismatch-cleavage analysis confirmed the presence of point mutations in the p53 gene in these cell lines. These mutations occurred in highly conserved regions of the p53 protein and were found to be homozygous. The study also showed that mutations in the p53 gene are common in colorectal cancer, with 8 of the 10 cell lines showing clear evidence of mutation. This suggests that p53 mutations are present in about 50% of colorectal cancers, though this may be an underestimate. The data also indicate that p53 mutations are likely to be at least 70 or 80% in frequency. The study highlights the importance of p53 mutations in colorectal cancer and their implications for diagnosis and treatment.P53 mutations are common in colorectal cancer. Immunohistological staining of primary colorectal carcinomas with p53-specific antibodies showed p53 overexpression in about 50% of malignant tumors, while benign adenomas were negative. Analysis of 10 colorectal cancer cell lines revealed that six expressed high levels of p53, which were found to be mutant. In two of these four cell lines with lower p53 expression, point mutations were still detected. This indicates that p53 overexpression is synonymous with mutation, but some mutations may not be detected by simple immunohistochemical analysis. Mutation of the p53 gene is one of the most common genetic changes in colorectal cancer. Understanding the genetics and biology of colorectal cancer is crucial for developing new prevention and treatment strategies. The p53 gene, located on chromosome 17p, is a key genetic change in colorectal cancer. Mutations in the p53 gene are found in a high proportion of lung, breast, and other tumors. Studies show that many human tumor-derived cell lines express elevated levels of p53, which can be explained by mutated forms of p53 that stabilize the protein. Immunohistochemical studies with monoclonal antibodies to p53 showed that a high proportion of colorectal carcinomas stained with these antibodies, while normal colonic epithelium was uniformly negative. Analysis of p53 protein expression in 10 colorectal cancer-derived cell lines showed that six expressed high levels of p53, which were found to be mutant. The remaining four cell lines did not express detectable levels of p53 protein, but all contained p53 mRNA. Direct sequencing and chemical-mismatch-cleavage analysis confirmed the presence of point mutations in the p53 gene in these cell lines. These mutations occurred in highly conserved regions of the p53 protein and were found to be homozygous. The study also showed that mutations in the p53 gene are common in colorectal cancer, with 8 of the 10 cell lines showing clear evidence of mutation. This suggests that p53 mutations are present in about 50% of colorectal cancers, though this may be an underestimate. The data also indicate that p53 mutations are likely to be at least 70 or 80% in frequency. The study highlights the importance of p53 mutations in colorectal cancer and their implications for diagnosis and treatment.