As cholesterol is metabolized, a potent stimulant of breast cancer is created -- one that fuels estrogen-receptor positive breast cancers, U.S. researchers say. Senior author Dr. Philip Shaul, professor and vice chair for research in pediatrics at the University of Texas Southwestern Medical Center in Dallas and a member of the Harold C. Simmons Comprehensive Cancer Center, says a multidisciplinary team discovered that the cholesterol metabolite 27-hydroxycholesterol promotes tumor growth in estrogen-receptor positive breast cancers -- the most common type of breast cancer. Estrogen-receptor positive breast cancer was previously believed to be stimulated primarily by the female sex hormone estrogen and it is commonly treated using endocrine-based medications that starve tumors of estrogen, Shaul said. The discovery of 27HC as another driver of breast cancer may explain why endocrine-based therapy is often unsuccessful, providing a new target for therapy, the researchers say. "This information can be used to develop new therapies that inhibit 27HC action or production, or increase its metabolism, in effect cutting the cancer off from a key growth stimulator," Shaul says in a statement. Implications of the research, published in Cell Reports, are significant, Shaul says. One million new cases of breast cancer are diagnosed each year in the United States and about two-thirds of those are hormone receptor-positive -- meaning they contain receptors for the hormones estrogen and/or progesterone, the American Cancer Society calculates. Estrogen receptor-positive breast cancer is particularly prevalent following menopause. Resistance to commonly used endocrine-based therapies occurs frequently.