Mutation of p53 is a common event in colorectal cancer and can result in cellular accumulation of p53 protein and induction of p53 antibodies. We investigated the association of colorectal cancer with alterations in p53 DNA, protein and serum antibody levels to determine their prognostic value in colorectal cancer. Colorectal cancer patients (n=167) who underwent surgery in Taipei Veterans General Hospital from January 1999 to December 2000 were enrolled [age 62.91+/-12.61 years (range: 22-85); 111 (66.5%) males]. Of these, 20 were stage I (12%), 54 stage II (32.3%), 58 stage III (34.7%), and 35 stage IV (21%). Median follow-up was 36.3 months (range: 4-58). p53 alteration was detected by DNA sequencing from exon 5 to 9 and loss of heterozygosity (LOH) at two microsatellite markers near p53; and demonstrating intratumoral accumulation of p53 protein and detection of serum p53 antibodies using ELISA. p53 mutation frequency was 41.9% (70/167). Of 127 informative cases for LOH analysis, 73 (57.5%) tumors that had LOH had at least one microsatellite marker. Genetic p53 alterations were found for 56.3% of cases when LOH and DNA sequencing methods were combined. Genetic p53 alterations were associated with advanced tumor stage and tumor differentiation. Overexpression of intratumoral p53 and anti-p53 antibody positivity were 44.9% and 28.1%. The presence of p53-Ab was associated with p53 mutations (chi2 test, 42.9% vs. 17.5%, p=0.001), but not with overexpression of intratumoral p53 protein. The mutations at exon 6 (57.1%) and 7 (53.3%) were associated with presence of serum p53-Ab. Of 132 potentially cured patients, 3-year disease-free survival (DFS) was affected by: advanced TNM stage (I, II, III: 90%, 84%, and 41%), genetic p53 alteration (89% vs. 43%), intratumoral p53 accumulation (71% vs. 56%), and preoperative CEA level >5 ng/ml (74% vs. 58%). In multivariate analysis, genetic alteration of p53 was the most significant independent prognostic factor [hazard ratio (HR) = 6.09; 95% confidence interval (CI): 2.45-15.11], followed by advanced tumor stage (HR = 3.93; 95% CI: 2.14-7.23), and preoperative CEA >5 ng/ml (HR = 1.98; 95% CI: 1.12-3.17). Genetic alterations in p53 but not intratumoral p53 protein accumulation or p53-Ab appear to play a significant role in the progression of colorectal cancer.