There is a consensus that diabetes is associated with a spectrum of breast cancers but the underlying mechanisms are largely unknown. On the other hand, there are ongoing debates about the risk association of insulin use with cancer. We have briefly reviewed recent related research on exploration of risk factors for breast cancer and diabetes and also link between them. Epidemiological studies have shown an association between diabetes mellitus and breast cancer: there is a twofold increased risk for breast cancer in women with late onset diabetes. Hyperinsulinemia and hyperglycemia are biomarkers for insulin resistance. Both of these disorders are critical to the initial development and progression of breast cancer. The hyperinsulinaemia seen in late onset diabetes may promote breast cancer because insulin is a growth factor for human breast cancer cells. At least four mechanisms may associate diabetes mellitus and breast cancer: activation of the insulin pathway, activation of the insulin-like growth factor (IGF) pathway, altered regulation of endogenous sex hormones and altered regulation of adipocytokines. © Global Science Publications. © 2014 Elsevier B.V., All rights reserved.