NEW YORK (Reuters Health) - Adding to evidence that hormone replacement therapy (HRT) can potentially raise a woman's risk of breast cancer, a new US study links recent, long-term HRT with a heightened risk of the disease.

Researchers found that HRT with estrogen alone or estrogen-plus-progestin was associated with a 70% increase in breast cancer risk when the therapy was taken for 5 years within the 6 years preceding the cancer diagnosis.

The findings build on previous research showing a link between long-term HRT and breast cancer and help clear up the question of whether combination HRT and estrogen-only HRT carry similar risks, the study's lead author told Reuters Health.

"I think the evidence is now quite strong that both types" are associated with breast cancer risk, said Dr. Emily White of the Fred Hutchinson Cancer Research Center in Seattle, Washington.

In addition, the study of about 1,300 women found that HRT use had a particular link to lobular breast cancer, the form of the disease that begins in the breast's lobules. It is far less common than ductal breast cancer, which begins in the milk ducts.

White's team found that women who were recent, long-time users of HRT faced a three-fold risk of lobular cancer compared with women who never used HRT. These women also had about a 50% increase in the risk of ductal cancer, according to findings published in the February 13th issue of the Journal of the American Medical Association.

The risk of lobular cancer was also elevated among women who were currently using combination HRT, regardless of duration. White said the reasons are unclear, "but that's what our data show."

And, her team notes in the report, two previous studies found a similar risk with current use of combination therapy.

Exactly why there was a particularly strong link between lobular breast cancer and HRT is unknown, according to White. A possible explanation, she noted, is the fact that lobular cancer is more likely than ductal cancer to test positive on hormone-receptor tests--meaning the tumor needs estrogen and progesterone to help it grow.

According to White, studies on the link between HRT and breast cancer--along with recent research doubting the benefits of HRT for women with heart disease--indicate that "we need to re-evaluate the risks and benefits associated with HRT."

She noted that the large, ongoing US study known as the Women's Health Initiative is expected to produce a new summary of the risks and benefits of HRT use in the next few years.

"In the meantime," White said, "I think it's less certain than it was a few years ago that the benefits outweigh the risks."

The established benefits of HRT include protection against the bone-thinning disease osteoporosis and treatment of hot flashes associated with menopause.

SOURCE: Journal of the American Medical Association 2002;287:734-741.

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