Estrogen-Only Therapy May Protect Against Breast Cancer, Research Suggests

Estrogen, a hormone known to fuel breast cancer, may protect against the disease in some cases, according to a study that found the therapy reduced the risk in women who took it after a hysterectomy.

The trial of 7,645 women showed that those on estrogen, sold as Premarin by Pfizer Inc. (PFE), for six years and then stopped were more than 20 percent less likely to develop breast cancer and die from the disease than those who never took the hormone therapy. The study is published online in the Lancet Oncology.

The research draws from the Women’s Health Initiative, a U.S.-sponsored study of disease and disability in postmenopausal women, and source of the 2002 findings that found women who took Pfizer’s Prempro, a combination of estrogen and progestin, for menopause symptoms, had a higher breast-cancer risk. Earlier studies had pointed to estrogen as raising that danger. Today’s finding may help dispel confusion surrounding the hormone therapies, said Garnet Anderson, a study author.

“We have not done the greatest job of distinguishing between the hormone therapies,” said Anderson, principal investigator of the Women’s Health Initiative Clinical Coordinating Center based at Fred Hutchinson Cancer Research Center in Seattle, in a March 5 telephone interview. “Estrogen alone for women with a prior hysterectomy has a very different risk profile then estrogen plus progestin.”

The Women’s Health Initiative study of Prempro included menopausal women with uteruses and was halted in 2002 because of the cancer risk, leading to a decline in sales of hormone replacement therapy pills.

Menopause Symptoms Therapy

Still, Anderson said that women should only take estrogen to relieve their menopausal symptoms like hot flashes and not to protect against breast cancer. Estrogen may cause strokes and blood clots. And in today’s study, the hormone wasn’t found to be protective in women with a strong family history of breast cancer or a history of benign breast disease, those most likely to take medicines to prevent the cancer, the authors said.

The researchers in the study included women who had their uterus removed and took either estrogen or a placebo. They were part of the Women’s Health Initiative Estrogen-Alone Trial that was stopped in 2004, a year earlier than planned, because of an increased risk of stroke.

In today’s study, the researchers found that women taking estrogen were 23 percent less likely to develop breast cancer compared with those taking a placebo during an overall follow-up period of about 12 years. Those in the estrogen group who did develop breast cancer were 63 percent less likely to die from the disease than those in the placebo group.

Reason Unknown

Anderson said it’s unknown why estrogen works to lower breast cancer risk in women who have had a hysterectomy.

In an accompanying comment, Anthony Howell, a professor of Breast Medical Oncology and director of the Genesis Breast Cancer Prevention Center at the University of Manchester in the U.K., and Jack Cuzick, with the Center for Cancer Prevention at Queen Mary University of London, said estrogen levels fall during menopause. Any precancerous cells in the breast may then adapt to the lower estrogen and when estrogen levels increase, rather than growing the tumors may actually die off, they wrote.

Today’s findings suggest that estrogen is most beneficial for women 50- to 59-years-old to ease menopausal symptoms, Howell said in a March 2 e-mail. Older women should avoid taking the hormone therapy because estrogen may increase the risk of strokes and heart attacks.

The results are “clearly very reassuring for women,” he said. “For the first time they demonstrated a significant reduction in breast cancer risk and a significant reduction in deaths from breast cancer.”

The Premarin family of drugs generated $1.01 billion in sales last year, Pfizer said on Jan. 31.

To contact the reporter on this story: Nicole Ostrow in New York at nostrow1@bloomberg.net

To contact the editor responsible for this story: Reg Gale at rgale5@bloomberg.net

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