Pfizer Inc.'s hormones, once used by millions of women to ease menopause symptoms, almost doubled the death risk from breast cancer, a U.S. study found.
The findings from the U.S.-funded Women's Health Initiative are the first to tie Pfizer's hormone replacement therapy Prempro, already linked to higher rates of breast cancer and heart disease, to increased mortality from tumors.
Pfizer, the world's largest drugmaker, on Tuesday won its sixth of 13 jury cases over Prempro's health risks an hour before the research was reported by the Journal of the American Medical Association. Previous studies suggested tumors fueled by hormone therapy were less aggressive and easier to treat. Pfizer gained Prempro in its $68 billion purchase of Wyeth last year. The hormones had annual sales of more than $2 billion before the study was halted in 2002, leading many women to stop treatment.
"You have more cancers, you have more advanced-stage cancers. And you aren't having just more favorable cancers," lead researcher Rowan Chlebowski, from the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, said. "Women should think critically about if they need this, if their symptoms are significant, and if they would persist."
Researchers tracked 12,788 women for almost eight years after the trial was stopped and found 678 cases of invasive breast cancer, including 385 for women taking hormones and 293 with a placebo. Investigators calculated there were 2.6 deaths caused by breast cancer for every 10,000 women taking hormones each year, compared with 1.3 deaths for those on a placebo.
The findings conflict with previous studies showing breast cancers in women taking hormone therapy had a lower risk of death, said Christopher Loder, a spokesman for New York-based Pfizer.
"We stand behind the current, science-based guidance in Prempro's label, which advises doctors to prescribe the medicine at the lowest effective dose and for the shortest duration," Loder said.
Prempro is a combination of hormones used to replace those the body stops making when a woman enters menopause, triggering symptoms such as hot flashes and mood swings. It is made of Premarin, an estrogen gathered from the urine of pregnant horses, and progestin, which reduces the risk of uterine cancer linked to the use of estrogen alone.
The decline in hormone use after the Women's Health Initiative results were initially released led to a drop in breast-cancer rates, with about 100,000 fewer invasive tumors detected from 2002 to 2007 than expected, said Chlebowski, chief of medical oncology at the University of California, Los Angeles, School of Medicine. With a 10-year mortality rate of about 20 percent, the reduction in hormone use may have prevented about 20,000 deaths, he said.
It is likely that the risk of dying from breast cancer was underestimated and will increase with time, wrote Peter Bach, from Memorial Sloan-Kettering Cancer Center's health outcomes research group, in an editorial accompanying the study.
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