Impact of interactions between normal and transformed epithelial cells and the relevance to cancer

The majority of human cancers are initiated when a single cell in an epithelial sheet becomes transformed. Cell transformation arises from the activation of oncoproteins and/or inactivation of tumor suppressor proteins. Recent studies have independently revealed that interaction and communication between transformed cells and their normal neighbors have a significant impact on the fate of the transformed cell. Several reports have shown that various phenomena occur at the interface between normal and transformed epithelial cells following the initial transformation event. In epithelia of Drosophila melanogaster, transformed and normal cells compete for survival in a process termed cell competition. This review will summarize current research and discuss the impact of these studies on our understanding of how primary tumors emerge and develop within a normal epithelium.