Decline in breast cancer: Not just because of hormone therapy

However, researchers led by Brian Sprague, Ph.D. have conducted a reevaluation of the post-WHI landscape that suggests otherwise.

"We found that the change in hormone therapy use only accounted for a decline of about 3 percent, so there's another 4 percent that is being caused by something we do not yet know," said Sprague, a postdoctoral fellow at the University of Wisconsin.

Results of this study were presented at the American Association for Cancer Research Frontiers in Cancer Prevention Research Conference, held Dec. 6-9 in Houston.

In 1991, the National Institutes of Health established the WHI to address the most common causes of death, disability and deterred quality of life among 15,730 postmenopausal women -- cancer, cardiovascular disease and osteoporosis.

Results of the WHI demonstrated in 2002 that hormone therapy is linked with an increased risk of breast cancer. Other studies have confirmed this relationship, and many women have stopped taking hormone therapy due to concerns about the potential risk of cancer. At the same time, the incidence of breast cancer has declined, which researchers attribute to the decrease in hormone therapy use.

After conducting a thorough literature review of the decline in hormone use and the decline in breast cancer incidence, Sprague and colleagues estimated that 42 percent of the decline in incidence of breast cancer was linked to the cessation of hormone therapy use.

Sprague said that additional studies are needed to determine the source of the remaining decline in breast cancer cases.

"This does not mean that women should start taking hormones again, but there appear to be additional factors that have contributed to the decline in breast cancer," he said.