Since the report by Beatson1 in 1896 of human mammary tumor regression occurring after bilateral oophorectomy, much interest has developed in the hormonal dependence of these tumors. Subsequently, it has been shown that a wide variety of both ablative, eg, adrenalectomy and hypophysectomy, and additive, eg, estrogen, progestin, androgen, and glucocorticoid, endocrine therapies are effective in causing regressions of tumors in certain patients with breast cancer. The importance of hormonal therapy lies in the fact that patients who respond to such therapy not only have palliative relief of symptoms, but they also have prolonged survival when compared with patients who do not respond. Unfortunately, only a third of unselected patients with breast cancer can be expected to have an objective response to endocrine manipulation. During the years, several clinical features have been empirically derived as useful indices to predict which patients would respond more often to endocrine therapy. These