Adipose tissue is an endocrine organ; it secretes adipokines and inflammatory cytokines and aromatizes androgen precursors to estrogen. Obesity enhances cancer risk. Many factors may be attributable, including increased leptin, reduced adiponectin, increased inflammatory cytokines such as interleukin (IL)-6 and tumor necrosing factor (TNF) alpha, and related metabolic disorders such as insulin resistance with hyperinsulinemia and increased insulin-like growth factor (IGF)-I. High estrogen levels, low sex hormone binding globulin (SHBG) and higher levels of androgens result in higher tumor proliferation. The higher risk for cancer has only been proven for specific situations and specific cancers, however. Breast cancer risk in obese women is only increased in postmenopausal women, but not in premenopausal women, for example. Here we review the current knowledge connecting obesity to cancer risk.