Obesity is commonly associated with insulin resistance which leads to progressive increases in fasting glucose levels and subsequent compensatory hyperinsulinemia in an attempt to normalize the hyperglycemia. This hyperinsulinemia and high levels of insulin-like growth factor 1 (both circulating and local) secreted by adipocytes in obese persons increase the risk of cancer. Finally, when the pancreas can no longer produce insulin, type 2 DM develops and exogenous insulin may be given to control high sugar levels.
The increased relative risk for diabetic individuals compared to nondiabetics is 2.5-fold for liver cancer, 2.22-fold for endometrial cancer, 1.5–2.0-fold for pancreatic cancer and non-Hodgkin's lymphoma, and 1.2–1.5-fold for biliary tract, renal, bladder, breast and bladder cancer, and oesophageal adenocarcinoma.
As shown in the study by Facchini et al , those that are in the most insulin-sensitive tertile have not a single case of cancer, CAD, stroke, hypertension or DM and the other 2 tertiles with more insulin-resistance have progressively more cases of above end points clearly indicate the importance of insulin-resistance in causing these chronic diseases. Therefore, it is important to detect insulin-resistance early and improve it so that the above chronic diseases can be prevented. A relatively simple way to detect insulin-resistance is to calculate TG/ HDL-C ratio. If this ratio is > 3.5, insulin-resistance is present  and there is also increased risk for cardiovascular disease (CAD, hypertension, stroke) and cancer.
Westley RLand May FEB: A Twenty-First Century Cancer Epidemic Caused by Obesity: The Involvement of Insulin, Diabetes, and Insulin-Like Growth Factors. Int J Endocrinol. 2013; 2013: 632461.
 Facchini FS, Hua N, Abbasi F, et al: Insulin Resistance as a Predictor of Age-Related Diseases. J Clin Endocrinol Metab 2001; 86: 3574–3578.
 McLaughlin T, Reaven G, Abbasi F, et al.: Is there a simple way to identify insulin-resistant individuals at increased risk of cardiovascular disease? Am J Cardiol 2005;96:399-404.