Epithelial self-defense against cancer

During the initial stage of carcinogenesis, transformation occurs in a single cell within an epithelial monolayer1,2. However, it is not clearly understood what happens at the interface between normal and transformed cells during this process. Are those transformed cells always accumulated in epithelia or are they eliminated from normal epithelial environments? In Drosophila melanogaster, normal and transformed cells often compete with each other for survival. For example, when Lethal giant larvae (Lgl)-knockout cells are surrounded by wild-type cells, Lgl-knockout cells die by apoptosis3,4. When Src-activated cells are surrounded by wild-type cells, Src-activated cells are basally extruded and leave the epithelium5. These phenomena are called 'cell competition', which has been intensively studied in Drosophila6,7,8. However, it was not known whether comparable phenomena also occur in mammals.