The study was done over a period of 10 years, 1996-2005 and it included 562 mammary cancer patients. Of the 562 cases, 100 cases of invasive mammary carcinoma included in this study were investigated from an immunohistochemical point of view. The p53 overexpression was more frequently seen in patients under 50 (23 cases, that is 54.76%), compared to those over 50 years old (19 cases, that is 45.24%). The positive p53 tumors were more often over 2 cm big. The invasive ductal carcinomas were p53-positive in 40 cases (44.44%) of all invasive ductal carcinoma cases, and the invasive lobular carcinomas were only positive in two cases (20%) of all mammary invasive lobular carcinoma cases. Most cases that had the overexpression of the p53-protein (30 cases that is 71.43%) had a high histological degree (G3), and only 12 cases (28.57%) had a low histological degree (G1 and G2). The overexpression of the p53-protein was present in all cases that had a heterogeneous phenotype (with one of the hormonal receptors being negative), in over half of the cases that had both hormonal receptors negative (59.37% of ER-/PR- phenotype cases) and in only 21.05% of cases that had ER+/PR+ phenotype. The association of the p53 overexpression (p53 over 10%), with the HER2 (2+ or 3+ score) overexpression was seen in seven patients of the 100 invasive mammary carcinoma cases included in this study. Consequently, 16.66% of p53 positive cases had associated positivity for HER2. Most cases that were p53 positive had an increased proliferation activity, as determined with Ki67. The Ki67 immunostaining analysis has made it clear that this marker has positivity presence in all cases. The vast majority of cases had a nuclear marking to Ki67, but two cases (2% of cases) had a cytoplasmatic / membrane staining.