The p53 tumor suppressor gene regulates progression of cell cycle at G1-S transition and inhibits the growth of tumor. The wild-type p53 protein is not detected in normal cells by low level and a short half-life. However, the increased level
of immunohistochemically detectable p53 protein provides a marker for mutation of p53 gene, which is the most frequently affected gene detected in many types of human cancers. Mutation of p53 involves not only a loss of function of wild-type p53 activity but also a gain of function as an oncogene. Colorectal cancer is characterized by frequent deletion of chromosome 17p close to the p53 locus and by point mutation of p53 locus, and then hemizygous loss of normal p53
allele. There is little information regarding the relationship of p53 expression to clinicopathological variables of colon cancer. In this study, the intracellular content of p53 protein was determined immunohistochemically to study the relation between p53 expression and clinicopathological variables. In addition, the value of P53 as a prognostic indicator of colon cancer was also investigated. Paraffin-embedded tissue specimens from 61 patients who underwent resection for
primary untreated colorectal carcinoma were examined for the incidence, pattern and intensity of p53 protein by immunohistochemical method using monoclonal antibody(Ab-6). p53 protein was detected in 36 out of 61 (59.0%) adenocarcinomas of the colorectal cancer and the most frequently expressed patterns of immunoreactivity of
p53 were moderate in intensity in 17 cases(47.2％) and were diffuse in pattern in 25 cases(69.4%). There is no correlation between p53 expression and sex, age, Dukes’ stage and histologic grade of the tumor A trend was seen towards a high rate of p53 expression in left sided cancers as compared to right sided ones(62.5% vs. 46.2％), however, it was
not statistically significant(p>0.05). Among the patients with radical resection of the tumor, 9(28.1%) of 32 patients with p53-positive tumors and 4(19.0%) of 21 patients with p53-negative ones had recurrences, which might imply that the patients
with p53-positive tumors had a greater relative risk of death compared to those with p53-negative tumors, although statistically insignificant. Two-year survival of p53 positive and P53 negative patients were 63.5% and 70.3% respectively, but there was no difference in survival between them. p53 mutation is a frequent event in human colorectal carcinoma as shown in this study, but it is not yet clear whether p53 protein is a significant independent predicator of aggressiveness and progressin of colorectal cancers. The results suggest the necessity for further study of analysis of p53 gene and protein molecules in attempting to determine whether assessment of the status of p53 in tumor will become a part of
potenital prognostic marker.
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