Catenin is a cytoskeletal protein, divided into three subtypes: α, β, and γ,  which is related to Wnt signaling and cell adhesion mechanism. Beta-catenin is a 92 kD protein normally found in the cytoplasm of the cell in the submembranous location. Mutations in the beta-catenin gene result in nuclear accumulation of this protein. Nuclear accumulation of this protein has been demonstrated in fibromatosis (desmoid tumors) of the breast and abdomen and, therefore, is useful in differentiating from other spindle cell neoplasms that may occur in these locations.^1-4