Abstract 5259: Bazedoxifene plus conjugated estrogen improves metabolic health and reduces mammary gland epithelial proliferation in an ovary intact rat model of obesity and breast cancer risk

Background: The majority of women risk eligible for primary breast cancer prevention with tamoxifen or aromatase inhibitors refuse uptake due to concerns about side effects, especially vasomotor symptoms. Tamoxifen may also have detrimental metabolic effects in overweight/obese women. Duavee™, a complex of bazedoxifene (BZA) and conjugated estrogen (CE), is FDA approved for relief of hot-flashes and prevention of osteoporosis. Preclinical studies suggest favorable metabolic effects in ovariectomized animals and potential for breast cancer risk reduction. A single arm clinical trial found reduction in Ki-67 and mammographic density such that BZA+CE is being further evaluated in a Phase IIB trial of peri and early postmenopausal women with vasomotor symptoms who are at high risk for breast cancer. Here, in a companion study, we assessed the effect of BZA+ CE on metabolic health and cancer risk in a rat model of carcinogen induced ER+ tumors and high fat diet induced obesity. Methods: Rats received 50 mg/kg N-methylnitrosourea at 7 weeks to increase mammary tumor risk and were fed a high fat diet (46% kcal fat) to promote obesity. At 16 weeks lean and obese rat were selected based on % body fat and were then randomized to 8 weeks of daily oral vehicle control or 3mg BZA + 0.07mg CE/kg body weight. Systemic metabolic variables were measured at 16 and 24 weeks, and RNA from mammary glands analyzed by gene expression microarray (Affymetrix). Results: BZA+CE resulted in systemic as well as mammary changes indicative of improved metabolic health, including: reduction in total and visceral fat (p