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Decline in Breast Cancer Diagnoses Follows Decline in Hormone Therapy Use, Recent Data Confirms

Latest Data From Kaiser Permanente and California Cancer Registry Shows Drop

OAKLAND, CA -- December 7, 2006 -- Research scientists at the Northern California Cancer Center and Kaiser Permanente's Division of Research have found significant reductions in both the use of hormone replacement therapies and the incidence of breast cancer in California in the years following the release of the 2002 Women's Health Initiative (WHI) trial results.

The data appear in the November 20 issue of the Journal of Clinical Oncology.

Previous studies have shown that long-term use of hormone therapy is linked to increased risk of breast cancer. For example, the WHI randomized trial and other studies discovered that estrogen plus progestin hormone therapy use increased a woman's risk of breast cancer.

This new analysis, the first to use the most recent 2004 California Cancer Registry data, supports the theory that women who discontinue hormone therapy use may reduce their chances of being diagnosed with breast cancer.

"Hormone therapy use dropped 68 percent between 2001 and 2003, and shortly thereafter we saw breast cancer rates drop by 10 to 11 percent. This drop was sustained in 2004, which tells us that the decline wasn't just a fluke," notes Dr. Christina A. Clarke, the Northern California Cancer Center scientist who led the study.

In the current study, researchers examined yearly prevalence of hormone therapy use and breast cancer incidence from 1994 to 2003 for women ages 50 to 74 in Kaiser Permanente's Northern California Region and in the 2004 California Cancer Registry. They found consistent evidence of corresponding trends in decline in both hormone therapy use and breast cancer incidence.

"We can't say that changes in hormone therapy use caused the decline in breast cancer, because these data don't link hormone users directly to breast cancer diagnoses, but they are certainly suggestive," adds Dr. Lisa Herrinton from Kaiser Permanente's Division of Research. "If it holds up over time, a 10 percent decline in breast cancer incidence is really striking. It amounts to an annual reduction of about 10,000 breast cancer cases in women aged 50 to 74."

Similar studies on the decline of breast cancer incidence in the United States will be presented by different researchers at the San Antonio Breast Cancer Symposium next week, though only data from 2003 is presented. The Northern California Cancer Center/Kaiser Permanente study includes data through 2004, and it provides information on hormone therapy for the same population.

From their analysis, researchers maintain that breast cancer incidence trends need to be monitored closely in regard to patterns of hormone therapy use. "Based upon what we know about the biology of hormone therapy, the declines make a lot of sense, and we want to continue to track these parallel trends," says Clarke.


SOURCE: Kaiser Permanente

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