CTNND1 (p120 Catenin, Catenin delta 1) is a member of the Armadillo protein family, which functions in adhesion between cells and signal transduction. CTNND1 stabilizes the epithelial adherens junction, an E-cadherin based complex that controls tissue integrity. Loss of CTNND1 is associated with cancer progression. Along with downregulation of e-cadherin, cytoplasmic IHC staining is observed in lobular breast carcinomas (and not invasive ductal carcinomas), with redistribution from the membrane to the cytoplasm. In normal epithelial cells as well as in invasive ductal carcinomas of the breast, CTNND1 staining is expected to be on the cell membrane. References: J Cell Sci 2013 126:3515; J Mamm Gland Biol Neopl 2016 21(3):81; Li, 2014; Li, 2010; Histopath 2016 68:57; Am J Surg Path 2007 31:427.