Mutations of the TP53 gene induce the production of an abnormal protein (p53) with a prolonged half-life allowing its detection by monoclonal antibodies and leading to a development of serum p53 autoantibodies. We have quantified the protein p53 in 196 cytosols of primary breast cancer tissues, by an immunoluminometric method and searched for p53 autoantibodies in the sera of 101 patients, by an immunoenzymatic assay. The median value has been chosen as cut-off (0.26 ng/mg protein). 18.4% of tumors had a p53 level < 0.10 ng/mg protein, and 8.2% had a p53 level > or = 2.5 ng/mg protein (range: 0.43.37). We found a significant difference between p53 distribution (p = 0.003) and median level (p = 0.001) in ductal and lobular carcinomas. The p53 median levels were significantly different between the grade III versus the grade I tumors (p = 0.01) and versus the grade II tumors (p = 0.008). An inverse correlation was obtained between p53 levels and ER (p = 0.003) alone or with PR (p = 0.006). p53 autoantibodies were detected in 7.9% of cases (8/101). This p53 study shows correlations with some poor prognostic factors, but would require further evaluation to better define the patient groups with poor prognosis. The p53 detection autoantibodies is neither correlated with the p53 cytosolic assay nor with prognostic factors of breast cancer, and should therefore not be used for patient the selection of the patient groups with poor prognosis.