Abstract 4873: Genistein and soy isoflavone isolate decreased tumor incidence and multiplicity in a Sprague-Dawley ER-positive breast cancer model

This study evaluated the chemopreventive efficacy of the pure soy isoflavone genistein and of a soy isoflavone mixture (PTI G-4660) containing roughly 90% genistein in an ER-positive breast cancer model in rats. Female Sprague Dawley rats were injected i.v. with N-nitroso-N -methylurea (MNU) at 50 days of age. In a model examining the effects on cancer initiation, promotion, and progression, rats were fed either a standard Teklad diet or a diet supplemented with genistein (200 or 2000 mg/kg diet) beginning at 43 d of age. Supplemented or standard diets were administered continuously thereafter until the end of the study. In a separate study testing the effects on progression, rats were administered standard Teklad diet or diet supplemented with PTI G-4660 (2000 mg/kg diet) beginning at 55 d of age. All rats were weighed weekly, palpated for mammary tumors twice per week, and checked daily for signs of toxicity. The studies were terminated 126 d after MNU treatment and tumors were weighed. After 126 days, genistein at 200 and 2000 mg/kg diet decreased tumor incidence in a dose-dependent fashion by 15 and 20% (p