Cooperation between cancer cells

Cancer cells secrete growth factors that induce proliferation, protect against apoptosis and the immune system or promote neo-angiogenesis [1]. As they are diffusible (Fig. 1), the growth factors produced by a cell can be used by other neighbouring cells, an example of cooperation among cancer cells [2]. A conceptual problem arises: a non-producer cell can exploit the growth factors secreted by its neighbouring producer cells without paying the cost of production; hence non-producers should have a proliferation advantage and spread in the population. How can intra-tumour cooperation be maintained then? Why do not non-producer mutants drive producer cells to extinction? EVOLUTIONARY PERSPECTIVES