Epidemiologic studies have proposed a link between obesity, type 2 diabetes, and cancer. The pathophysiologic mechanisms involved in the development of type 2 diabetes, namely hyperinsulinemia and insulin resistance, have also been implicated in cancer development. Patients with type 2 diabetes are reported to have a worse response to cancer chemotherapy, have more complications, and have a poorer prognosis than patients with cancer without diabetes. Studies also have reported that insulin, insulin secretagogues, and metformin may have effects on tumor growth. Given the escalating worldwide prevalence of obesity and type 2 diabetes, their relationship to cancer has generated great interest and research across many fields of medicine.