Postmenopausal women who've had a hysterectomy and have used estrogen therapy for 15 years or more appear to be at higher risk of breast cancer, a new study found.

    The new findings, published in the May 8 issue of Archives of Internal Medicine, help to clarify researchers' understanding of the potential link between estrogen therapy and breast cancer.

    Hormone supplements were once thought to help postmenopausal women postpone age-related ills. Past studies that looked at estrogen taken with the hormone progestin have linked this combination to an increased risk of breast cancer among postmenopausal women.

    But results released in April from the U.S. government's Women's Health Initiative (WHI) found no significant connection between estrogen therapy alone ¡ª an option only for women who've had a hysterectomy ¡ª and breast cancer in women who took the hormone for seven years.

    "Estrogen only causes cancer after prolonged exposure," said Dr. Wendy Y. Chen, lead researcher of the new study, who's with Brigham and Women's Hospital and Dana Farber Cancer Institute, in Boston.

    Chen's team believes the effect of estrogen is cumulative. "We found that there was a 42 percent increased risk for all types of breast cancer for women who had used estrogen alone for 20 or more years," she said. For the study, Chen and her colleagues collected data on 28,835 women who were part of the Nurses' Health Study.

    Given these findings, women need to consider whether they want to use estrogen over an extended period, Chen said. "For women who use estrogen alone, and have been on it for more than 10 years, they would want to consider how much longer they want to remain on estrogen," she said.

    Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City, thinks these findings show that the current guidelines for estrogen use make sense.

    "Current guidelines for estrogen therapy hold true," Wu said. "The current recommendation for estrogen therapy is to use the lowest effective dose for the shortest duration of time."

    (Agencies)