Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Background: It remains unknown whether erbB2 expression and hormone receptor status predict the invasive potential of ductal carcinoma in situ (DCIS) of the breast. Objectives: To examine erbB2 and estrogen/progesterone receptor (ER/PR) status in the precise areas where DCIS turns into invasive ductal carcinoma (IDC). Subjects and methods: Eighty-seven cases of breast malignancies harboring contiguous regions of DCIS and IDC were selected. Separate histological samples from the DCIS and the neighboring IDC were obtained using tissue microarrays. The erbB2 and ER/PR statuses were assessed using immunohistochemistry (erbB2 and ER/PR) and fluorescence in situ hybridization (FISH only erbB2). Results: The expression of erbB2 did not differ in the DCIS and IDC components of the breast tumors (p=0.35). There was good agreement in sample-by-sample comparisons of erbB2 (intraclass correlation coefficient [ICC]=0.78), PR (ICC=0.61) and ER (ICC=0.70) expression in the DCIS and IDC components. Conclusion: Our findings suggest that the expressions of erbB2 and ER/PR do not differ in the contiguous regions from DCIS to IDC. (Int J Biol Markers 2009; 24: 238-44)244238244Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2008/08536-9, 2008/02469-8]