Diabetes and Cancer

Diabetes mellitus and associated conditions such as hyperglycaemia and hyperinsulinaemia have been associated with risk of several cancers including pancreatic, colorectal, endometrial and liver cancer. Associations identified with other cancer sites in epidemiological studies are suggestive. It is unknown whether the association between diabetes and some cancers is largely due to shared factors such as obesity and inactivity, or whether the specific metabolic derangements associated with diabetes such as hyperinsulinaemia and hyperglycaemia directly increases cancer risk. Nevertheless, as obesity and physical inactivity are the main determinants of insulin resistance and hyperinsulinaemia, the public health importance of these findings is clear. Evidence-based interventions that increase physical activity and reduce obesity in clinical settings and in communities are likely to have beneficial effects on risk of diabetes and several common cancers. Of particular interest for aetiological research are the studies that have shown that the insulin-like growth factor I (IGF-I) axis is related to cancer risk. Increases in circulating levels of IGF-1 have been observed in several epidemiological studies of colorectal, prostate and breast cancer. Clinicians who treat cancer patients must consider the cardiac, hepatic, renal and neurological complications that are commonly seen among patients with diabetes. Evidence from clinical trials and population-based studies suggests that, after a cancer diagnosis and treatment, patients with diabetes experience higher mortality and cancer recurrence rates than those without. Patients with hyperglycaemia or diabetes who undergo cancer treatment may be more likely to experience certain side effects than patients who do not have hyperglycaemia or diabetes. A growing body of evidence suggests that metformin protects against the development of certain cancers and may improve prognosis in patients with breast cancer. Randomized trials to test these hypotheses are currently ongoing.