Clinical outcomes in breast cancer are likely influenced by modifier genes that affect tumor dormancy versus progression. The Bin1 gene encodes a nucleocytosolic adapter protein that suppresses neoplastic cell transformation and that is often attenuated in human breast carcinoma. Recent mouse genetic studies indicate that Bin1 loss cooperates with ras activation to drive progression of mammary carcinoma, establishing Bin1 as a negative modifier of tumor progression in breast cancer. In this study, we investigated whether immunohistochemical losses of nuclear Bin1 proteins in cases of human breast cancer were correlated to progression status. In American and Japanese groups of low or middle grade breast cancers, losses were associated with reduced survival and increased nodal metastasis, respectively. Taken together with recent findings from mouse genetic studies, these findings encourage further evaluation of the potential utility of Bin1 as a clinical prognostic marker in breast cancer.