Chronically elevated proliferation as a risk factor for neoplasia

Chronic disease conditions that are associated with elevated proliferation are well established as risk factors for cancer development. These may be due to viruses (for example, in the case of hepatitis and liver cancer), bacterial infections, parasite infestation or physical trauma. In addition to these exogenous agents there are also metabolic abnormalities that can contribute, caused by genetic or epigenetic influence. In the latter case, an increase in serum levels of the hormones oestrogen, testosterone and insulin may be of special importance. The present review concentrates attention on factors that induce elevated cell turnover and for which there is epidemiological and/or experimental evidence of a link with neoplasia, with particular stress on the individual organ or tissue level.