Process analysis of carcinogenesis: concept derivation of the tissue function "preservation of a homogeneous gene expression".

A new system for maintaining homogeneous gene expression in tissue and for destroying through apoptosis nonconforming cells is introduced. This functionality is called the "similarity comparison." Accordingly, the survival of mutated cells is hindered due to reduced gene expression. That, in turn, maintains the homogeneity of the tissue and prevents tumors from developing. The concept of the similarity comparison is that every stationary cell in every tissue constantly screens the gene expression of its neighbors. Cells process the signals, and when the difference between neighbors exceeds some threshold, a signal is triggered. An under-expressing cell then either increases its gene expression or apoptosis occurs. The oversight role of the similarity comparison can, under certain conditions, be disrupted, such that mutated cells in the tissue can survive. This is possible only when surrounding normal cells exhibit reduced gene expression. In this case, the normal cells and mutated cells have similar gene expression, and the signal for apoptosis is not triggered. The mutated cells survive, and a tumor can develop. The importance of the similarity comparison as an oversight mechanism is studied. Examples are considered.