While some forms of hormone replacement therapy (HRT) have been found to increase breast cancer risk, treatments with estrogen may protect some women against the disease. A new study found that women who had a hysterectomy and took estrogen-only pills for about six years were more than 20 percent less likely to develop breast cancer. The results are based on a follow-up to the Women's Health Initiative, a 10-year study of more than 10,000 women taking HRT. The trial was halted in 2004 amid concerns that the therapy increased women's risk of stroke and breast cancer. “The story is pretty clear about estrogen plus progestin -- no matter the age of the women, estrogen plus progestin increases [the risk of] breast cancer, heart disease, stroke and blood clots,” said Garnet Anderson of the Fred Hutchinson Cancer Research Center in Seattle. Researchers continued to monitor the women for another five years and found that those who took estrogen had a 23 percent lower risk of breast cancer compared to those who took placebo. According to the study, preventive effects of taking estrogen-only HRT went just to women who had a hysterectomy. The reduced risk of breast cancer applied only to women who were not already at risk for the disease, researchers wrote in the journal Lancet Oncology. “If women are suffering from serious menopause symptoms and have had a hysterectomy, then estrogen alone is a reasonable approach,” said Anderson. “These new data suggest that women don't have to be afraid of taking estrogen-only HRT.” Researchers suggested breast tissue cells including precancerous ones may become more susceptible to estrogen after menopause, an effect which may discourage cell growth.