Proliferation defines the exponential increase in the number of cells within a tissue and requires simultaneous cell growth and division. Since both, cell growth and cell division can occure independent from each other to either produce a single larger cells or many progressively smaller cells, cell proliferation is not synonymous with either of the two.
Stem cells usually undergo proliferation followed by differentiation to generate or regenerate tissue either during development or after damage or cancer.
Proliferation depends on a balanced rate of cell growth and division to maintain a constant cell size during the exponential increase of the cell number. However, proliferation strongly depends on the availability of nutrients and is tightly controlled by gene regulatory networks. The normal cell proliferation and the pathologic consequences occurring if the system malfunctions are critical to many areas of medicine, from embryogenesis, to tissue repair up to oncogenesis. In contrast to normal cells, cancer cells own an excessive cell proliferation because they increase proliferative signal transmission and avoid growth suppressor. The main reason for excessive cell proliferation and tumor development are modified transcription factors, which act as key regulators for cell cycle-dependent proliferation. Some of these transcription factors such as p53, CDK4, Cyclin d1 are easily detectable and are of great importance as tumor markers in diagnostics and cancer research.