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WHI Intranet Site
Breast Cancer after Use of Estrogen plus Progestin
Dietary Trial (1994-2005)
Hormone Trials (1994-2004)
Calcium/Vitamin D Trial (1994-2005)
Observational Study (1994-present)
Breast Cancer after Use of Estrogen plus Progestin in Postmenopausal Women
Abstract of scientific paper in The New England Journal of Medicine
Following the release of the findings from the Women’s Health Initiative Estrogen Plus Estrogen Hormone Trial (E+P), use of hormone therapy in the United States fell sharply. During that time, rates of breast cancer also went down, suggesting a relationship between stopping hormone therapy and the decrease in breast cancer. However, some researchers felt that the drop in breast cancer was too fast to be explained by lower hormone use. Others thought that the decreased rates might be due to the drop in mammography rates during the same period.
WHI investigator Rowan T. Chlebowski, M.D., Ph.D., Principal Investigator of the Torrance, CA clinical center, and other WHI scientists examined data from WHI participants to help explain the reason for the drop in breast cancer rates. In this analysis, they looked at new breast cancer incidence, hormone use, and mammography use over the same period of time in two groups of WHI women: those in the E+P Hormone Trial and those in the Observational Study. Their findings are reported in the Feb 4, 2009 issue of the New England Journal of Medicine.
Findings from this new analysis confirmed that the risk of breast cancer associated with estrogen plus progestin use goes down significantly once these hormones are stopped. In addition, they found that the increase in breast cancer risk seen with longer use of estrogen plus progestin is even higher than previously estimated. A woman continuing E+P hormone therapy after about 5 years doubles her annual risk of breast cancer.
The study findings suggest that the decline in breast cancer risk seen after hormone therapy was stopped was unrelated to the drop in mammography use during those same years. “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 Dr. Chlebowski.
“Postmenopausal women and their physicians should consider these findings when weighing the risks and benefits of combined estrogen plus progestin use, especially if they plan to take the medication for more than five years” said Dr. Chlebowski.
Combined estrogen plus progestin longer than 5-years nearly doubles subsequent breast cancer risk each year.
The marked decline in breast cancer risk soon after stopping hormones is not related to changes in mammography use.
These findings support the hypothesis that the recent reduction in breast cancer incidence is primarily related to a decrease in estrogen plus progestin use.