PURPOSE: We purpose to determine the correlation of HER-2/neu and paxillin expression in ductal carcinoma in situ (DCIS), invasive ductal carcinoma with ductal carcinoma in situ (IDC with DCIS) and mucinous carcinoma. METHODS: To evaluate the expression of HER-2/neu and paxillin, the immunohistochemical staining was performed for 13 cases of DCIS, 13 cases of IDC with DCIS and 6 cases of mucinous carcinoma. RESULTS: The DCIS and IDC were associated with infiltration of the inflammatory cells, especially in the comedo type and solid type of tumor. In cases with infiltration of the inflammatory cells, HER-2/neu and paxillin were strongly expressed. When comparing the expression level of HER-2/neu from adjacent normal tissue between DCIS and IDC with DCIS, expression of HER-2/neu was similar to that of normal tissue adjacent to DCIS. However, in the adjoining normal ductal epithelial cells, paxillin was highly expressed in cells of all of the tumor types, and especially for IDC with DCIS. HER-2/neu and paxillin were not expressed in mucinous carcinoma cells in all cases. CONCLUSION: HER-2/neu in the DCIS and IDC with infiltration of inflammatory cells shows higher expression than non-inflammatory DCIS and IDC. If normal duct epithelial cells show a high level of HER-2/neu expression, the epithelial cells have a high probability of transformation into anaplastic cells. However, paxillin appears to have no value as a prognostic factor. The difference of expression of HER-2/neu between IDC with DCIS and DCIS suggests a different origin of tumor cells. The growth pattern of mucinous carcinoma cell is different from the that of DCIS or IDC cell, which grow slowly.