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A new study provides strong evidence that the dramatic decline in breast cancer cases in women over 50 since 2002 can be attributed to the decline in hormone replacement prescriptions for menopausal women.

Statistics analyzed by a large team of researchers and just published in the New England Journal of Medicine show that the frequency of breast cancer diagnoses began falling after prescriptions for hormone replacement were curtailed following studies that showed cancer risks. The decrease in cases persisted into 2003 and up to the present, confirming that the trends are related.

The study says an estimated 16,000 fewer cases of breast cancer are being diagnosed each year because of the drop in hormone use, a complete reversal of a decades-long increase in cases.

The findings also explain another mystery about breast cancer — why the number of cases rose steadily for decades beyond what could simply be attributed to better detection methods. Increasing hormone use likely played a key role, researchers said.

Underscores the Dangers of Widely Using Untested Drugs

Two of the drugs studied were Premarin® and PremproTM, both of which have been targeted in numerous lawsuits against their pharmaceutical company maker. Premarin is a combined estrogenprogestin preparation, and Prempro is a conjugated equine (derived from a horse) estrogen drug.

Reaction to the study has been widespread. Some scientists are saying the findings underscore the danger of drug therapies becoming widely used before they have been thoroughly tested. Others said the findings should encourage more women to stop hormone use altogether or to continue at the lowest dose and for the shortest time necessary.

“We believe that the data are most consistent with a direct effect of hormone-replacement therapy on preclinical disease,” the study concluded, “but this conclusion does not rule out some contribution from changes in screening mammography. In any case, attempts to understand the rapid reduction in incidence using theoretical models of breast-cancer evolution and the effects of screening and treatment — such as those of the National Cancer Institute’s Cancer Intervention and Surveillance Modeling Network — may lead to new insights into the development and prevention of breast cancer.”

These findings come on the heels of the UK’s Million Women Study, which has found that hormone replacement therapy increases the risk of ovarian cancer and endometrial (the lining of the womb) cancer. That study also supports the US study showing an increase in breast cancer.

SOURCE: New England Journal of Medicine, April 2007, http://content.nejm.org/cgi/content/full/356/16/1670
Premarin and Prempro are trademarks of Wyeth Pharmaceuticals, Inc.