Evidence that steroid hormones can play an important role in gynecological malignancies has been provided since 1896, when Sir George Beatson reported remissions in two patients with breast cancer after bilateral oophorectomy. All steroid hormones act on their target cells by binding to cellular receptors. Thus, the presence of the appropriate receptor in a tissue can be taken as a good indication that that tissue is hormonesensitive. Following these observations, many studies in this century have demonstrated that the knowledge of the steroid-receptor status of gynecological tumors, especially breast and endometrial cancer, can offer important information about the differentiation, response to endocrine therapy, and prognosis of the disease.