PURPOSE: It has been reported that the antibody against p53 is detected in a certain proportion of patients with malignancies. The authors designed this study to investigate the correlation between appea rance of the serum p53 antibody and tissue expression of the mutant p53 protein in primary breast carcinomas. METHODS: We conducted assays for the serum p53 antibody in 76 patients with primary breast cancer by using a sandwich enzyme linked immunosorbent assay (ELISA). Immunohistochemical assays for tissue expression of the p53 mutant protein were also undertaken in the same patients, and the results were analyzed according to the patients' outcomes and the clinical/histopathologic parameters. RESULTS: Antibody against p53 was detected as a high titer in the sera of 12 patients (16.9%) whereas the mutant p53 protein was detected in 41.1% of the breast cancer tissues. We found a significant correlation between serum p53 antibody status and tissue expression of the mutant p53 protein (p=0.019), whereas serum p53 antibody status did not correlate with any clinical/histopathologic parameters except the histologic grade of the tumors. The antibody against the p53 protein was more frequently detected in the patients with undifferentiated tumors. In the survival analysis, the serum p53 antibody had no significant correlation with recurrence of the disease or with patient survival. CONCLUSION: It seems likely that accumulation of p53 protein in tumor cells may induce an immune response with the appearance of p53 antibodies in the sera of cancer patients. However, serum p53 antibody status failed to discriminate high risk population of breast cancer patients.