Hormones are chemicals produced by group of cells which act at another place (cells or organs) of the body. Hormones modulate the expression of growth factors, oncogenes, tumor suppressor factors, cytokines and other components involved in signal transduction, cell cycle checkpoints, and cell death (apoptosis). Recently, hormones have been found to be an etiological agents in many malignant tumors especially breast, prostate, endometrial, ovarian cancers and others. The mechanism of carcinogenesis is through inducing cell proliferation, mutation and stimulating replication of the mutated cells. Tumors may produce signs and symptoms at sites distant from the primary tumor or its metastases and these are referred to as paraneoplastic syndromes. There are many hormonal agents used in treatment of patients with cancer. The primary use of these agents is in hormonally responsive cancers such as breast, prostate or endometrial carcinomas. For these hormonally related cancers, clinical trials in this field are ongoing aiming for developing less toxic newer generations of hormonal agents with the same efficacy of chemotherapy or radiotherapy.