Women who stopped taking the postmenopausal hormone combination of estrogen plus progestin experienced a marked decline in breast cancer risk which was unrelated to mammography utilization change, according to a study from the Women's Health Initiative led by a Los Angeles Biomedical Research Institute (LA BioMed) investigator that was published today in The New England Journal of Medicine.

Breast cancer in the United States began to decline in 2003, after the Women's Health Initiative's initial findings that combined hormone therapy was related to higher risk of breast cancer and heart problems.

Using data from the Women's Health Initiative's randomized trial and observational study cohort of postmenopausal women on combined hormone therapy, the researchers in the study published today also found that continued use of combined estrogen plus progestin after five years about doubles subsequent breast cancer risk each year.

"These findings support the hypothesis that the recent reduction in breast cancer incidence in the United States is predominantly related to a decrease in combined estrogen plus progestin use," said Rowan T. Chlebowski, M.D., Ph.D., a LA BioMed chief investigator and lead author for the study. 

The National Heart, Lung and Blood Institute provided grants to support this study of data from the Women's Health Initiative. The National Institutes of Health established the Women's Health Initiative in 1991 to address the most common causes of death, disability and impaired quality of life in postmenopausal women, including the use of combined hormone therapy. That part of the study was halted in 2002 when researchers saw surprisingly higher rates of heart problems and breast cancer in women taking the hormones.

"Postmenopausal women and their physicians should consider these findings in weighing the risks and benefits of combined estrogen plus progestin use, especially if the women plan to take the medication for more than five years," said Dr. Chlebowski.