Obesity is a known cause of metabolic syndrome which includes Type II diabetes, hypertension, and dyslipidemia. It is well documented that insulin resistance contributes to the mortality and the incidence of metabolic syndromes including central obesity, dyslipidemia, hyperglycemia and hypertension. Both obesity and diabetes are emerging topics for researchers to consider as having a possible causal association with cancer since the two factors have been viewed as risk factors for cancer. The present paper introduced the hypothesis of a possible causal relationship between obesity, insulin resistance and cancer and reviews relevant existing studies in this area. More efforts and studies are needed to clarify the mechanisms and the common risk factors which might be incorporated into interventions to prevent cancer and cardiovascular diseases as top causes of death.