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Breast Cancer Health Center

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New Clues on Breast Cancer Decline

Increases and Drops in Breast Cancer Rates Tied to HRT Use
WebMD Health News
Reviewed by Louise Chang, MD

July 24, 2007 -- New research shows a dramatic drop in breast cancers in 2003 and 2004, while offering some of the best evidence yet that a parallel drop in the use of hormone replacement therapy (HRT) was responsible for the decline.

The findings make it clear that since 1990, breast cancer rates have been moving in tandem with hormone therapy use, researcher Andrew G. Glass, MD, of Kaiser Permanente Northwest tells WebMD.

The declines were confined to estrogen-receptor positive (ER+) breast cancers, which are sensitive to the same hormones used in menopausal hormone replacement therapy.

The study appears in the Aug. 1 issue of the Journal of the National Cancer Institute.

“This was strong biologic evidence that the cancer decline was related to hormone use,” he says.

Breast Cancer, HRT, and Mammography

Using Kaiser Permanente’s extensive patient database, Glass and colleagues were able to review 26 years' worth of health information on 7,386 breast cancer patients.

They also compared breast cancer incidence rates among health system members with mammography usage and hormone therapy use between 1980 and 2006.

Among women aged 45 and older, breast cancer rates rose by 25% from the early 1980s to the early 1990s and continued to rise at a slower rate (15%) through 2001.

Breast cancer rates among health plan members dropped by 18% between 2003 and 2004.

Other key findings from the study:

  • The 25% rise in breast cancers during the 1980s corresponded with sharp increases in both mammography screening and HRT usage during the decade.
  • The 15% rise in breast cancers from 1992 to 2002 corresponded with a leveling off of mammography usage and a continued increase in the use of menopausal hormone therapy.
  • The dramatic drop in breast cancers starting in 2003 paralleled a precipitous drop in HRT usage following the 2002 release of a widely reported government study questioning the safety of menopausal hormone therapy. Mammography screening rates did not change during the period.

Does HRT Cause Breast Cancer?

But if breast cancers take years and even decades to develop, as experts say, why would the sharp decline in HRT use in one year be reflected in a dramatic drop in breast cancers the next?

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