The Role of Diabetes and Diabetes Treatments in Colorectal Cancer Mortality, Incidence, and Survival

Type 2 diabetes mellitus (T2DM) and colorectal cancer are major causes of morbidity and mortality worldwide. T2DM and colorectal cancer share common risk factors related to westernized lifestyles, including high body mass index and central adiposity, low physical activity, cigarette smoking, and diets characterized by low intake of fruit and vegetables and high intake of red and processed meats and refined grains and sugars. Epidemiologic studies show that T2DM is quite convincingly associated with higher risk of colorectal cancer incidence and mortality, even after accounting for their shared risk factors. Whether T2DM is related to poorer prognosis after colorectal cancer diagnosis is less understood and controversial, although some larger studies suggest poorer prognosis among patients with T2DM. The impact of diabetes treatments, such as metformin or insulin, on colorectal cancer risk also is characterized poorly. This review describes studies on the association of diabetes and its treatments with colorectal cancer mortality, incidence, and survival. Potential clinical and biological explanations for these associations are explored.