These are structurally related intra-cellular proteins that bind to steroid hormones such as oestrogens and progesterone and relay their signals leading to down-stream gene expression (signal transduction). Cancers dependent on steroid hormones include breast, prostate, testicular, ovarian and endometrial cancer, which result from deregulation of hormone secretion, signalling and receptor action.The concept of steroid hormone playing an important role in carcinogenesis was first demonstrated by surgical removal of the ovaries, which was followed by reduced levels of circulating hormones and remarkable improvement in women with breast cancer.