Here, we show that loss of apical membrane polarity in hyperplastic lesions of MMTV-Neu mammary glands or in human DCIS leads to intermixing of these molecules and allows Erbin to interact with NHERF1, Ezrin and HER2 initially within the basolateral membrane and then more diffusely throughout the plasma membrane. This evidence concerns the gene ERBB2 and ductal breast carcinoma in situ.