More evidence links breast cancer, hormone therapy

Hormone replacement therapy increases the risk of breast cancer, especially among women receiving a combination of estrogen and progestin, a major British study found.

The report, published in this week's edition of The Lancet, a British medical journal, concluded that women now receiving hormone replacement therapy had a 22 percent higher risk of death from breast cancer compared to women who were not receiving therapy.

However, a U.S. medical specialist who was not involved in the British study said it did not settle the question of whether estrogen by itself posed a significantly higher risk of cancer.

The Lancet report was based on the "Million Woman Study" which surveyed 1,084,110 women in the United Kingdom aged 50 to 64. They were recruited between 1996 and 2001, and tracked for cancer incidence and death.

Professor Valerie Beral, director of the Cancer Research UK Epidemiology Unit and lead author of the study, said there was "overwhelming evidence" that the combination therapy was associated with a greater cancer risk.

Among 1,000 postmenopausal women who do not use hormone replacement therapy, or HRT, there will be around 20 breast cancer cases among women between the ages of 50 and 60, Beral said.

In every 1,000 women who begin 10 years of HRT at the age of 50, there will be five extra cases among estrogen-only users, and 19 among estrogen-progestin combination users, she said.

"The evidence is now compelling that estrogen plus progestin is more deleterious to the breast than estrogen alone," said Dr. JoAnn Manson of the Harvard University Medical School.

"However, there continues to be controversy about whether unopposed estrogen increases the risk of breast cancer," said Manson, who was not involved in the British study.

Manson said the Women's Health Initiative, a U.S. government-sponsored study of 16,608 postmenopausal women ages 50 to 79, "will provide conclusive answers to this question in the next two years."

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Revision date: 12 December 2007
Last revised by Amalia K. Gagarina, M.S., R.D.