Effects of raloxifene in a guinea pig model of leiomyomas

Raloxifene reduces the size of leiomyomas in estradiol-exposed guinea pigs. Leiomyomas are fibroid tumors of the uterus, and they can develop from continuous high levels of estrogen in the body. Researchers placed estradiol-secreting implants in guinea pigs to induce leiomyoma formation, removed the implants, then replaced them. Some animals also received raloxifene, an estrogen blocking drug. The tumors grew in the presence of estradiol, regressed without estrogen stimulation, and regressed with simultaneous estradiol and raloxifene treatment. Leiomyomas appear to require estradiol exposure to continue growing, and raloxifene appears to block this process.