β-catenin is a multifunctional protein that plays a vital structural role in cadherin-based cell adhesion and is an important transcriptional activator of canonical Wnt-mediated gene expression. Dysregulation or mutational activation of the β-catenin signaling is a critical event in the development of human cancer, including breast cancer. Immunofluorescence staining was used to visualize localization of β-catenin and activated β-catenin in human ERBB2-overexpressing ER-negative breast cancer cells (HCC202). The presence of nuclear-activated β-catenin in these breast cancer cells was correlated with a decrease in cell proliferation upon inhibition of β-catenin signaling. For details, see article by Schade and colleagues on page 4474.