WASHINGTON — Women who take estrogen and progestin after menopause not only increase their chances of getting breast cancer but also seem to face a small increased risk of dying from the disease, according to new results of a landmark federal study.
The study of more than 16,000 women who were followed for about 11 years produced the first powerful evidence that deaths from breast cancer were more common among hormone users, apparently because those who took the once-popular medication for more than five years were more likely to receive a diagnosis of more advanced tumors.
The hormone combination was long touted as essentially a pharmaceutical fountain of youth for menopausal women. But eight years ago, the federally funded Women's Health Initiative revealed that its benefits were outweighed by risks, such as heart disease and breast cancer, causing hormone use to plummet. Still, many experts thought that hormones primarily increased the chances of developing smaller, less-threatening tumors and that hormone users would not be at greater risk of dying from cancer.
The new analysis of the Women's Health Initiative, published in today's issue of the Journal of the American Medical Association, was based on 11 years of data instead of the original 5.5 and found that women who took the hormones were just as likely as those who did not to develop more difficult-to-treat tumors and were more commonly found with tumors that had begun to spread.
"It had been said that the cancers would have a more favorable prognosis," said Rowan T. Chlebowski of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, who led the analysis. "This is the first time we are able to talk about mortality, and there were significantly more deaths from breast cancer."
Coupled with research published last year that found women who took hormones were about 70 percent more likely to die from lung cancer, the findings underscore the risks posed by the therapy, Chlebowski said. Millions of women still take hormones. "Women taking estrogen plus progestin are at greater risk from dying from the two leading causes of cancer death in women," Chlebowski said.
The findings surprised even some experts who have remained more supportive of hormone use. "This really is a paradigm shift," said Hugh S. Taylor, chief of reproductive endocrinology at Yale University.
Several experts stressed, however, that the absolute risk of dying from breast cancer was very low — in the new study 25 women died from breast cancer among those taking the hormones compared with 12 among those who took a placebo. The increased risk translates into about 1.3 additional deaths from breast cancer each year for every 10,000 women taking the hormones, the study found.