It is believed that knowledge of the receptor status of all three receptors (ER, PR, AR) may identify more accurately those patients with breast cancer who are most likely to respond to endocrine treatment (Brentani 1986, Langer 1990, Kuenen-Boumeester 1992, Isola 1993, Collett 1996). The gene discussed is ESR1; the disease is breast carcinoma.