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Taking estrogen plus progestin for just a year raises women's chances of having abnormal mammograms, says the latest report from a groundbreaking study of postmenopausal hormones.
In addition, the study found that breast cancers tended to be more advanced at diagnosis in women taking the hormones than in women on a placebo.
The mammogram finding raises questions about taking the hormone combination for even a short time to relieve hot flashes. Though most abnormalities seen on mammograms are not cancer, they often cause anxiety and lead to further testing, including biopsies.
''This is the first (study) that's really going to cause some women to really consider the risk-benefit ratio of short-term use,'' says lead author Rowan Chlebowski of the Harbor-UCLA Research and Education Institute.
Researchers halted treatment in the estrogen-plus-progestin arm of the government-sponsored Women's Health Initiative last year when they found that taking the hormones for four years or more increased breast cancer risk. The new report, in The Journal of the American Medical Association, is based on a more detailed analysis of the study's breast cancer data.
The study randomly assigned 16,608 postmenopausal women to take Prempro, the top-selling estrogen-plus-progestin brand, or a placebo. After the first year, 9.4% of women on Prempro had an abnormal mammogram, compared with 5.4% of those on placebo. And after 5 years, breast cancer was diagnosed in 245 women on hormones and 185 on placebo.
Women on hormones were 24% more likely to be diagnosed with breast cancer than women on the placebo. That equals eight extra cases per 10,000 women per year, a ''really quite small'' difference, says Chlebowski, a cancer doctor.
But the study casts doubt on the common notion that hormone users who get breast cancer do better than non-users. On average, breast cancers diagnosed in the hormone group were slightly larger and more likely to have spread.
The authors speculate that the differences between the hormone and placebo groups could stem from the fact that estrogen plus progestin increases breast density. A spinoff study evaluating breast density on the mammograms of a subset of participants may provide some answers, they add.
In an accompanying editorial, Peter Gann and Monica Morrow of Northwestern University's Feinberg School of Medicine write that the new findings ''provide further compelling evidence against the use of combination estrogen plus progestin hormone therapy.''
Wyeth Pharmaceuticals, Prempro's maker, says it is evaluating the report to determine whether labeling changes are needed.
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