Cancer incidence and mortality are higher among diabetic patients. This review examines the mechanisms, both general and site-specific, for this increase.
Hyperglycemia and
hyperinsulinemia, which are the major abnormalities that characterize diabetes, can promote
cancer via both independent and synergic mechanisms.
Insulin is both a metabolic
hormone and a
growth factor that promotes cell proliferation. When
insulin levels are increased due to either
insulin resistance or
insulin treatment, their mitogenic effect is more marked in malignant cells that frequently overexpress the
insulin receptor and, more specifically, its A
isoform that has predominant mitogenic activity.
Hyperglycemia provides energy for malignant cell proliferation and, via the peculiar energy utilization of
cancer cells, favors
cancer growth and neoangiogenesis. Additionally, diabetes-associated
obesity has
cancer-promoting effects due to mechanisms that are specific to excess fat cells (such as increased peripheral
estrogens, increased pro-
mitogen cytokines and
growth factors). Also fat-associated chronic
inflammation can favor
cancer via the cell damage caused by
reactive oxygen species (ROS) and via the production of inflammatory
cytokines and
transcription factors that stimulate
cancer growth and invasiveness. Finally, the multiple drugs involved in the treatment of diabetes can also play a role. Diabetes-associated comorbidities, tissue-specific
inflammation, and organ-specific dysfunctions can explain why the risk of
cancer can differ by tissue type among diabetic patients. The increased risk of
cancer-related mortality is moderate among individual patients with diabetes (RR = 1.25), but the pandemic nature of the disease means that a considerable number of lives could be spared through a better understanding of the factors associating diabetes and
cancer.