context and objective: breast cancer is thought to derive from progressively aberrant, non-invasive breast lesions, but it is not known exactly how invasive breast cancer develops from these lesions. the aim of this study was to verify the changes in c-erbb-2 and p53 protein expression between non-neoplastic ducts, ductal carcinoma in situ and invasive ductal carcinoma found in the same breast. design and setting: this was a cross-sectional study at centro de aten？？o integral à saúde da mulher, campinas, brazil. methods: fifty-six women with invasive ductal carcinoma and ductal carcinoma in situ in the same breast were included. the expression of c-erbb-2 and p53 proteins was assessed in non-neoplastic and neoplastic cells using immunohistochemical techniques. results: the c-erbb-2 protein was absent in non-neoplastic ducts but was present in 46% and 36% of in situ and invasive carcinoma components, respectively. only 2% of non-neoplastic ducts, and 18% and 16% of ductal carcinoma in situ and invasive carcinoma components, respectively, were positive for p53 protein. no significant difference in c-erbb-2 and p53 protein expression was observed between in situ and invasive components. the nuclear grade agreement between in situ and invasive carcinoma was very good. conclusions: the invasiveness of ductal carcinoma in situ seems to be independent of the her-2/neu and tp53 genes. the general features of an occurrence of breast carcinoma are formulated at the outset of carcinogenesis, and the her-2/neu and tp53 genes are involved.