Catenin is a cytoskeletal protein that is divided into three subtypes: α, β and γ, and is associated with Wnt signaling and cell adhesion mechanism. Beta-catenin is a 92 kD protein normally located in the cytoplasm of the cell in the submembranous localization. Mutations in the beta-catenin gene lead to nuclear accumulation of this protein. Nuclear accumulation of this protein has been demonstrated in fibromatosis (desmoid tumors) of the breast and abdomen and is therefore useful to differentiate from other spindle cell neoplasms that may occur at these sites.