The phenomenon of cell competition is an interactive process originally discovered in Drosophila; it is a developmental mechanism that identifies and eliminates cells that are weaker than their neighbours or have features that make them different or not well adapted to their surroundings. It appears to be an important homeostatic mechanism to contribute to the general fitness of developing tissues. Within this surveillance function cell competition appears to be responsible for the removal of malignant or aberrant cells that may appear during development, indicating that it normally functions as a tumour suppressing mechanism. Several recent studies from the vertebrate field indicate that cell competition also occurs in vertebrates where it performs similar functions. Thus it appears to be a universal mechanism of the Animal Kingdom responsible for the elimination of unfit or undesirable cells that may compromise the fitness or viability of the organism.

One appealing aspect of the cell competition phenomenon is its connection with tumorigenesis, which has been analysed both in Drosophila and in vertebrates. The role of cell competition as tumour suppressor derives from its general surveillance function described above; it recognises tumour cells as aberrant and proceeds to eliminate them. Studies in Drosophila have shown that the elimination of outcompeted cells occurs by regular apoptosis mediated by the activation of the Jun-N terminal Kinase (JNK) pathway that induces the function of pro-apoptotic genes like hid or reaper. As in Drosophila, cell competition in vertebrates also appears to have a therapeutic role in eliminating oncogenic cells in vitro and in vivo. Furthermore, compromising cell competition in the progenitors of T cells gives rise to lymphoblastic leukaemia that resembles closely the human disease.

One unexpected observation, made in Drosophila but also in the mouse is that programmed cell death (apoptosis), which normally functions as anti-tumour factor, can also act stimulating tumour growth. Secreted growth factors like Wingless (Wg) and Decapentaplegic (Dpp) in Drosophila and Prostaglandin E2 in mouse cells appear to be responsible for the growth stimulus. Since cell competition is an apoptotic phenomenon it has raised the possibility that it may also act stimulating tumour growth when there is a continuous flux of cells entering cell competition/apoptosis. The molecular mechanism behind this proliferative signalling from apoptotic cells has not been elucidated, although signalling pathways associated with apoptosis, like the JNK pathway, appear to be involved.

In the International Meeting on Cell Competition in Development and Cancer sponsored by the Fundación Ramon Areces, the leading figures in the field will get together to present the most recent results and have an open discussion about the general mechanisms and overall function of cell competition. Of special interest will be the presentation of new results establishing the role of cell competition in vertebrates. The links between apoptosis, cell competition and tumorigenesis, together with the molecular mechanisms of cell competition, will also be major themes of discussion.