Menopausal women taking combined hormone therapy have an elevated risk of being diagnosed with a more advanced stage of breast cancer and dying from it, according to a new US study.
Researchers conducted a new analysis of a landmark, federally funded clinical trial known as the Women's Health Initiative (WHI), which was halted in 2002 after data suggested women who took a combination of estrogen and progestin hormones faced a higher risk of breast cancer.
The study, published in this week's edition of the Journal of the American Medical Association, also found that women who previously used hormone therapy and discontinued it after the WHI was terminated still faced a slightly higher breast cancer mortality rate than women not taking hormones.
For their analysis, Rowan Chlebowski of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center and colleagues observed 16,608 postmenopausal women ages 50 to 79 years with no prior hysterectomy from 40 US clinical centers.
Their follow-up of about 11 years of WHI participants found that 385 women receiving hormones for an average of 5.6 years, or 0.42 percent, developed invasive breast cancer, compared with 293 women who received a placebo, or 0.34 percent.
A significantly larger fraction of the women in the hormone therapy group -- 81, or 23.7 percent -- were diagnosed after their breast cancer had spread to lymph nodes. In the placebo group, only 43 women, or 16.2 percent, were diagnosed at that stages.
Twenty-five of the women who received the hormone therapy died from breast cancer, compared to 12 deaths among those who received a placebo. That translated to one to two extra deaths from breast cancer each year for every 10,000 women who used hormone therapy rather than a placebo.
Researchers noted that in the WHI trial, unlike most observational studies, combined hormone therapy both increased the risk of breast cancer and interfered with breast cancer detection, hindering the detection of breast cancer and thus leading to diagnoses at more advanced stages.
"Now, with longer follow-up results available, there remains a cumulative, statistically significant increase in breast cancers in the combined hormone therapy group, and the cancers more commonly had lymph node involvement," the researchers said.
"The observed adverse influence on breast cancer mortality of combined hormone therapy can reasonably be explained by the influence on breast cancer incidence and stage."
They noted that the incidence of breast cancer substantially decreased in the United States after the WHI trial's results were initially reported eight years ago, which was attributed to a marked decrease in postmenopausal hormone therapy use.
"The adverse influence of estrogen plus progestin on breast cancer mortality suggests that a future reduction in breast cancer mortality in the United States may be anticipated as well," the researchers added.
In an accompanying editorial, Peter Bach of Memorial Sloan-Kettering Cancer Center in New York said "the available data dictate caution in the current approach to use of hormone therapy," namely because physicians are "ill-equipped" to anticipate its effects on long-term health.
"Clinicians who prescribe brief courses of hormone therapy for relief of menopausal symptoms should be aware that this approach has not been proven in rigorous clinical trials and that the downstream negative consequences for their patients are of uncertain magnitude," Bach added.
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