Diabetes mellitus (DM) and cancer are global health problems that constitute a major portion of spending for every health system. Epidemiological and experimental studies have demonstrated the interrelationship between type 2 DM (T2DM) and cancer in various tissues such as pancreas, colon, endometrium, ovary, and breast. The exact biological mechanisms by which DM may cause an increased risk of cancer are incompletely understood. The reason for a correlation may be attributed to different elements, including common risk factors between cancer and diabetes and possibly the biological links between the pathophysiology of the two diseases. Insulin resistance, hyperinsulinemia, hyperglycemia, increased levels of insulin-like growth factor, and the chronic inflammation associated with diabetes may increase cancer incidence and mortality in patients with T2DM. The aim of the current study is to review the literature on this subject to shed light on the possible relationships between T2DM and some site-specific cancers.