(NaturalNews) Hormone replacement therapy (HRT) may increase women's risk of developing breast cancer and interfere with cancer diagnostic techniques after as little as one year, according to a new large-scale study conducted by researchers from the Los Angeles Biomedical Research Institute and published in the journal Archives of Internal Medicine.
Researchers used data from 16,600 postmenopausal women who had participated in the National Institutes of Health's Women's Health Initiative (WHI), comparing those who underwent combined HRT as a treatment for menopause symptoms with those who were given a placebo. The study did not look at women who underwent estrogen-only HRT.
In combined HRT, women are treated with a combination of the hormones estrogen and progesterone.
The combined HRT treatment in the original WHI study was halted early in 2002, when researchers found that women undergoing the treatment had a higher risk of invasive breast cancer, heart disease and stroke. But analysis of those results suggested that it took at least five years for those problems to develop, and that they occurred mostly in older women.
The current study confirmed the WHI's conclusion that combined HRT led to one additional case of breast cancer per 1,000 treatments, but it also found evidence that problems could emerge more quickly than previously believed, and in younger women.
Most significantly, according to lead researcher Rowan Chlebowski, combined HRT increased women's risk of experiencing abnormal mammograms.
After only one year of combined HRT, women had a 4 percent higher chance of an abnormal mammogram than women not receiving HRT. After five years, their risk was 11 percent higher than those in the control group.
In absolute terms, this meant that while only 23 percent of the women in the placebo group had abnormal mammograms, 35 percent of the women in the combined HRT group did. Nearly twice as many women in the combined HRT group as in the placebo group - 10 percent as opposed to 6 percent - had breast biopsies ordered by their doctors. According to Chlebowski, this amounted to one "otherwise avoidable" biopsy for every 25 women taking combined HRT, and one abnormal mammogram for every 10 combined HRT patients.
In contrast to prior studies that found combined HRT relatively harmless for younger women, Chlebowski noted that "the finding may impact women just entering menopause as well."
Up to one year after the discontinuation of combined HRT, "adverse effects on mammogram and breast biopsy performance were seen even in younger women [in their 40s]," he said.
The rate of positive biopsies was slightly lower among women in the combined HRT group than women in the placebo group. This suggests that the early phases of combined HRT interfere with the ability of mammograms and biopsies to properly diagnose breast cancer.
This effect may come from the fact that combined HRT is well-known to thicken women's breast tissue; studies have shown that mammograms have more trouble detecting tumors in more dense breasts. But some researchers warned that the effects of HRT are complex, and that scientists do not necessarily understand them well.
"We have clinical trials that show women's mammograms over time, and anyone can see with a naked eye that the breast tissue has changed. There are so many hormone-sensitive cells in the breast," said Dr. Christina Clarke of the Northern California Cancer Center and the Stanford Comprehensive Cancer Center. "These mammograms are harder to read. It's concerning that mammography doesn't work as well in these women."
Chlebowski urged women who are considering HRT to "take the results of this study into consideration and consult with their physicians before undergoing even short-term hormone therapy."
Susan Kutner, of the Kaiser Permanente Santa Teresa Medical Center in San Jose, Calif., agreed. She encouraged women to consider not just the physical consequences, but also the psychological impacts of having to undergo more biopsies.
"Psychologically, it's a big deal for a woman to be told that there's something abnormal," she said.