WEDNESDAY, April 18 (HealthDay News) -- When millions of U.S. women tossed out their prescriptions for hormone replacement therapy in 2002, the rates of breast cancer started dropping almost immediately, U.S. researchers reported Wednesday.
Their findings coincided with an early-release report from the U.K. that showed women who took hormone replacement therapy (HRT) after menopause were 20 percent more likely to develop ovarian cancer or die from it than postmenopausal women who never took HRT.
The breast cancer report, published in the April 19 issue of the New England Journal of Medicine, looked at the incidence of breast cancer both before and after the news broke from the long-term Women's Health Initiative (WHI) study that HRT might be more damaging than helpful to a woman's health. Between 2001 and 2004, it shows, the overall incidence of breast cancer went down by 8.6 percent in postmenopausal women.
The U.K. study, published online Wednesday by The Lancet, looked at the long-running Million Women Study and determined that 1,000 additional women died from ovarian cancer between 1991 and 2005 because they were using HRT, and that 1,300 extra cases of ovarian cancer were diagnosed in the same period.
The researchers, from the Cancer Research UK Epidemiology Unit in Oxford, also found that after women stopped taking HRT, their risk of ovarian cancer returned to the same level as those who never used HRT.
For the U.S. study, experts suspect that HRT may have been fueling some breast cancers because that decline began soon after many women stopped using HRT.
"From 1975 to 2000, breast cancer incidence increased rather dramatically. While part of that increase was clearly due to the introduction of screening mammography, once you take out that effect, there is still a rather astounding increase of 30 percent," said Donald Berry, chairman of the department of biostatistics at the University of Texas M.D. Anderson Cancer Center in Houston.
"While there have been a number of theories put forward to explain the increase, it now looks like some of that increase is due to the use of HRT," Berry said. "When women stopped using HRT, it looked kind of like a market correction and the numbers went back down."
Initially, it appeared as if combination estrogen-progestin hormone replacement therapy was the answer to many ills. Researchers hoped that HRT would lower the risk of such serious illnesses as heart disease and dementia.
However, the WHI study, which included more than 16,000 postmenopausal women, was stopped early in May 2002 because HRT was increasing the risk of coronary disease, stroke and blood clots.
After the WHI trial was halted, many women stopped taking hormones. In fact, the use of HRT had dropped by 38 percent in the United States by the end of 2002. In 2001, 61 million prescriptions were written for hormone replacement therapy. In 2002, there were about 47 million prescriptions. By 2003, that number had fallen to 27 million, and by 2004 just 21 million, the study authors noted.
The rate of breast cancer started dropping soon after the WHI results in 2002, according to the new study.