They turned to a large French study in which 1,726 invasive breast cancers were diagnosed among 53,310 postmenopausal women from 1992 through 2005.
They took into account hormone use, types of hormones, when the therapy was started and how long it was taken, along with comparing users and non-users.
In addition to finding a 54 percent increased risk for those who took hormone therapy for two years or less within three years of the start of menopause, they also found that short-term treatment of two years or less that was started more than three years after the beginning of menopause didn't increase breast cancer risk. However, longer duration of use elevated risk, no matter when the therapy was begun.
The new study should serve as a warning, said Leslie Bernstein, director of the division of cancer etiology at the City of Hope National Medical Center in Duarte, Calif., who wrote an accompanying editorial.
"The missing piece is, 'How safe is it to take right after menopause in terms of breast cancer risk?'" Bernstein said.
The French study provides some answers, but more research is needed, she said. The regimens typically taken in France are different than those taken by most U.S. women, Bernstein noted. And French women often use skin patches, not oral pills.
Any woman who is taking hormone replacement therapy should check with her doctor to see what hormone formulation is involved if she wants to more accurately assess her breast cancer risk.
While noting that the 54 percent elevated risk found by the French researchers is "worrisome," Bernstein pointed to another study finding -- that once a woman stops hormone therapy, her risk over time declines to that of the general population.
"I see this paper as a warning," Bern
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