Abstract
B9L/BCL9-2, a novel beta-catenin-interacting protein, plays an important role in colorectal carcinogenesis by translocating beta-catenin to the nucleus and enhancing beta-catenin-T-cell factor-mediated transcription. To elucidate the role of B9L in breast cancers, we studied B9L expression in ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) of the breast immunohistochemically and compared it to the immunohistochemical expression of known proteins involved in breast carcinogenesis. In breast tissues, B9L immunoreactivity was present exclusively in the nuclei of normal and neoplastic ductal cells. In DCIS, immunohistochemical B9L expression was significantly associated with the tumor nuclear grade, comedo necrosis and the expression of ErbB2/HER-2, c-myc and p53. In IDC, B9L expression was correlated with ErbB2/HER-2 expression and tumor nuclear grade only. In both DCIS and IDC, immunohistochemical B9L expression was not related to the expression of cytoplasmic beta-catenin. We demonstrated that nuclear B9L expression was closely associated with the high nuclear grade cancer phenotype and the expression of ErbB2/HER-2 in breast cancers.