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TUESDAY, June 24, 2003 (HealthDayNews) -- Yet another study has found an apparent increased risk of breast cancer in older women who have taken combined hormone replacement therapy for at least five years.
The latest study, appearing in the June 25 issue of the Journal of the American Medical Association, found that the increased risk held true regardless of the pattern of progestin use, a hormone used in tandem with estrogen.
"I think the new study that we have just further characterizes risk of combined therapy," says Dr. Christopher Li, the lead author of the study, and an assistant member at the Fred Hutchinson Cancer Research Center in Seattle.
Adds Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in Baton Rouge, La., "This is just another piece of evidence that shows that combined estrogen/progesterone hormone replacement increases the risk of breast cancer. This is another example of why these two types of medicines used together should not be used, if at all possible, by women."
Hormone replacement therapy (HRT) is prescribed to control symptoms of menopause, such as hot flashes. Because estrogen increases the risk of endometrial cancer in women, it is taken with progestin, which mitigates that effect. HRT can either be taken continuously (estrogen and progestin every day) or sequentially (estrogen daily and progestin for about 10 days every month).
Last summer, a large study called the Women's Health Initiative found that women taking combined hormone therapy experienced a 26 percent increase in invasive breast cancer rates, compared to women taking a placebo. Because of this and other health risks, the trial using the two hormones together was stopped.
Most of the women participating in the WHI were taking continuous hormone replacement therapy. The new study assessed both continuous and sequential treatments by looking at HRT use in 975 women who had been diagnosed with breast cancer, along with 1,007 "controls" -- women who were free of the cancer.
Li and his colleagues found a 50 percent increased risk of invasive ductal carcinoma, which affects the milk ducts carrying milk to the nipple and represents about 80 percent of all breast cancers.
There was a 170 percent increased risk of invasive lobular breast cancer. Lobular breast cancer is the second most common type of breast cancer and involves the areas of the breast that contain the milk-producing glands.
Women who took combined HRT had twice the risk of hormone-receptor-positive breast cancer. These tumors need either estrogen or progesterone to grow.
Women who took "unopposed estrogen" -- or estrogen without progestin even for as long as 25 years -- did not have any greater risk of breast cancer, the study found.
"Unopposed estrogen was not associated with breast cancer even if it was used for a long period of time," Li says. "Combined therapy was associated with an increased risk of breast cancer. It didn't matter whether women took sequential or continuous. Both increased breast cancer risk but only if they had used it for five years or longer."
Adds Li: "Another thing that we found in our study is that women who are current users [of HRT] are at higher risk than women who are former users. But we didn't have that many people who were former users."
"Now that the WHI results have been published and there's a greater sense among women that maybe they should stop taking HRT, we'll be able to evaluate women who stopped HRT use," Li says. "Does their risk of breast cancer go back to baseline or will it stay elevated?"
The study has limitations, however. Even though the relative risk seems high, the absolute number of women in the study who were on HRT and developed breast cancer wasn't huge.
Also, Brooks points out, "it's an observational study," not the more rigorous randomized, placebo-controlled study.
"It doesn't have nearly the size or power that the Women's Health Initiative had," he says.
More information
The American Medical Women's Association and the American College of Obstetricians and Gynecologists have question-and-answer sections on HRT.
