Diabetes and cancer: epidemiology and potential mechanisms

Type 2 diabetes mellitus is an independent risk factor for cancer such as pancreatic, liver, colorectal and breast cancer. In addition, diabetes decreases the risk of prostate cancer. These associations have been found in numerous epidemiological studies, among them several prospective cohorts. However, such studies do not prove causality of the association and cannot exclude inadequate correction for known confounders (e.g. visceral fat) or the influence of unknown confounders. Thus, it is unclear whether the cancer risk is increased by the causes (e.g. the metabolic syndrome), the metabolic consequences (e.g. hyperglycaemia) or the therapy of diabetes; a question which is of major importance for therapeutic guidelines. Identification of the potential mechanisms by which the diabetes or its therapy accelerates or inhibits the development of cancer will help answering the question by providing biological plausibility. This review will summarize the evidence supporting the association of cancer and type 2 diabetes and discuss its potential causes.