BACKGROUND: Recent studies have conflicting results concerning the role of p53 protein related to the discovery that a wild-type of p53 is a nuclear protein that plays a role both as a tumor suppressor and may play roles in the control of transcription and as a negative regulator of cell growth, whereas mutant p53 supports tumor formation in experimental oncogenic settings and is overexpressed in some human tumors. The mutant p53 is abnormally stable, leading to increased expression. p53 has been most widely studied by the immunohistochemical method. p53 overexpression often found in some studies, but not always in other studies, have been shown to be an independent predictor of poor prognosis. METHODS: To evaluate a possible prognostic factor, we studied the expression of the p53 protein by an immunohistochemical method and compared these results with the established prognostic factors for breast carcinomas. RESULTS: 78 patients aged 28-69 were included in this study. The mean age was 46.3, and 53 patients out of 78 were less than 50 years old. There were 28 cases with tumor diameters of less than 2 cm, and 50 with tumor diameters of more than 2 cm. The most common pathologic type was an infiltrating duct carcinoma, 71 out of 78 cases (91.0%), and proportions of histologic grade I, II, and III tumors was 23 (29.5%), 41 (52.6%), 14 (17.9%), respectively. Cases with lymph node metastasis numbered 52 of 78 (66.7%). We observed a remarkable increase in the nuclear staining intensity at the invasive margins of some tumors, which may be linked to a higher incidence of proliferating cells. CONCLUSIONS: p53 overexpression was associated with tumor size (p<0.05), but was not associated with lymph node status, age, histologic grade, or estrogen receptor status.