Diabetes mellitus as a risk factor for cancer: stress or viral etiology?

Diabetes mellitus (DM) is a metabolic disorder. Currently over 230 million patients demonstrate already an epidemic scale of the disease. It is a lifelong progressive disease with a high mortality worldwide: every 10 seconds one patient dies on DM-related consequences. Whereas cardio-vascular complications are well-known for DM, it is relatively new consideration that diabetic patients are highly predisposed to cancer. Particularities of molecular pathomechanisms of cancer in diabetes are currently largely unclear. Disturbed glucose/insulin homeostasis is DM-specific stress factor resulting in increased production of Reactive Oxygen Species (ROS) and oxidative damage to chromosomal and mitochondrial DNA frequently observed in diabetic patients. Long-term accumulation of DNA mutations is well-acknowledged as triggering cancer. DNA-repair is highly energy consuming process which provokes increased mitochondrial activity. Particularly dangerous is a provoked activity of damaged mitochondria which leads to the "vicious circle" lowing energy supply and potentiating ROS production. Mitochondrial dysfunction is the well-acknowledged risk factor for neuro/degenerative diseases--one of possible pathomechanisms for various complications developed secondary to diabetes. At the same time, mitochondrial dysfunction might be implicated in pathomechanisms of diabetes-provoked cancer. There is a growing body of evidence that DM predisposes to almost all cancer types with some particular preferences. Frequently suffering from compromised immune response, diabetic patients is high-risk group for infectious disorders including viral infections. In its turn, viral infections are known to be implicated in cancer pathology. This review considers both stress and viral infections as possible etiology of cancer in diabetes.