Aims: (a) To assess the expression patterns of HER2/neu, steroid receptors (ER and PR), Ki67 and p53 in invasive ductal cancer (IDC) and IDC associated with carcinoma in situ (IDC/DCIS) and (b) to determine if there is a differential expression of these molecular markers between IDC and IDC/DCIS.

Materials and methods: Paraffin-fixed breast cancer samples, diagnosed with only one histological invasive tumor (IDC (n=130), and IDC/DCIS (n=36) were analyzed by immunohistochemical means. The non-parametric Mann-Whitney and chi2 tests were used to evaluate any statistical differences between different groups. Significance was assumed at p<0.05.

Results: A significant increase of the tumor grading was observed between IDC and IDC/DCIS (p<0.05). Her2/neu amplification was demonstrated in 49.6% of IDC compared to 31% of IDC/DCIS (p<0.05). ER expression showed no statistical differences between IDC and IDC/DCIS. The PR expression was demonstrated in 71% of IDC with significantly lower intensity than IDC/DCIS (p<0.05). The Ki67 expression was significantly higher (p<0.05) in IDC cases (64%) versus IDC/DCIS (49.7%). No differences were observed between IDC and IDC/DCIS for p53 expression.

Conclusion: We demonstrated significantly different expression patterns of Her2/neu, PR and Ki67 in IDC versus IDC/DCIS. Since these molecular markers play important roles in carcinogenesis and tumor progression, IDC/DCIS could be an important subtype of mammary invasive ductal cancer. Differences in expression of the evaluated markers might suggest a higher malignant potential of invasive carcinomas alone. The lower expression of Her2/neu and Ki67 in IDC/DCIS could implicate a less malignant behavior compared to a differentiated IDC. Additionally, these results might suggest that DCIS might be a malignant preform and the interaction with neoplastic tissue could result in an aggressive type of invasive tumor.