MayoClinic.com looks at the numbers behind falling breast cancer rates

ROCHESTER, Minn. — A new feature on MayoClinic.com provides context and answers questions about the connection between HRT and breast cancer rates raised by a recent study in the New England Journal of Medicine, which reported a 9 percent drop in breast cancer rates from 2001 to 2004 among women age 50 and older.

Researchers point to a major drop in women's use of hormone replacement therapy (HRT) as the likely reason for the decline in breast cancer rates. The sharpest decline — 7 percent — came in 2003. That's the year after a major national study of a combination hormone replacement therapy found the treatment increased the risk of breast cancer and heart disease. Many women were advised to stop taking HRT.

Like many medical discoveries, this new study answers some questions and raises several more. The new MayoClinic.com feature provides detailed answers to questions like:

Are researchers certain that the reduction in HRT is the reason for the decline in breast cancer rates?

It's probably too soon to be certain, and there's probably more than one reason for the decline. Estrogen, the main hormone replaced in HRT, is a growth simulator. It could be that some breast cancers linked to HRT are still occurring but just not evident because they are growing more slowly. More long-term follow-up is needed.

What other factors could contribute to the study results?

Some reports released between 2000 and 2003 questioned the value of mammogram screening, and mammography rates declined. Medications or medical treatments could play a role, too. For example, another study showed that calcium is related to a modest decrease in breast cancer rates. Women have been increasing the amount of calcium in their diets.

How much did the rate of breast cancer actually decline?

Media stories reported varying numbers about the decline in breast cancer incidence, up to 15 percent. That higher rate was for a specific subset of women in the study and doesn't accurately represent the overall decline in breast cancer rates.

Does the drop in breast cancer incidence mean no one should use hormone replacement therapy?

HRT is still an option for women with moderate to severe menopause symptoms. Further study is needed to refine recommendations so women can make informed decisions.

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