THURSDAY, Dec. 9, 2010 (HealthDay News) -- In a finding that seems to counter the prevailing wisdom that any form of hormone replacement therapy raises the risk of breast cancer, a new look at some old data suggests that estrogen-only hormone therapy might protect a small subset of postmenopausal women against the disease.
"Exogenous estrogen [such as hormone therapy] is actually protective" in women who have a low risk for developing breast tumors, said study author Dr. Joseph Ragaz, a medical oncologist and clinical professor in the School of Population & Public Health at the University of British Columbia in Vancouver.
With his colleagues, Ragaz took another look at data from the Women's Health Initiative (WHI) study, a national trial that has focused on ways to prevent breast and colorectal cancer, as well as heart disease and fracture risk, in postmenopausal women. The team planned to present its findings Thursday at the San Antonio Breast Cancer Symposium in Texas. Research presented at medical meetings is not analyzed by outside experts, unlike studies that appear in peer-reviewed medical journals, and all such findings should be considered preliminary.
Launched in 1991, the WHI includes more than 161,000 U.S. women between the ages of 50 and 79. Two groups were part of the trial -- women who had had hysterectomies and took estrogen alone as hormone replacement therapy and a group that took estrogen plus progestin hormone replacement therapy.
The combination therapy trial was halted in 2002 after it became clear those women were at increased risk for heart disease and breast cancer.
In the new look at the estrogen-only group, Ragaz said, "we looked at women who did not have high-risk features." They found that women with no prior history of benign breast disease had a 43 percent reduction breast cancer risk on estrogen; women with no family history with a first-degree relative with breast cancer had a 32 percent risk reduction and women without previous hormone use had a 32 percent reduced risk.
Overall, the 10,000-plus participants had a 20 percent reduction in breast cancer risk, a reduction that approached statistical significance, Ragaz said.
After their review, Ragaz said they concluded that using estrogen alone, particularly if begun in women less than 60 who don't have a uterus, can help reduce breast cancer risk.
The new review did not receive drug company funding, Ragaz said.
"Women without a uterus should be totally safe and benefit a great deal [with estrogen-only use]," he said.
Yet, more research is needed to find the best treatment regimen, decide who are the ideal candidates and to figure out exactly why the estrogen only reduces risk in some women, he said.
The findings don't actually include anything new, said Dr. Rowan Chlebowski, a WHI investigator who is chief of medical oncology/hematology at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center. The same results, he said, were published back in 2006, when the WHI investigators reported on the estrogen-only arm of the study.
"These results have been around for a long period of time," he said. But, he added that "you have to be cautious about interpreting subgroups."
To say estrogen is protective, Chlebowski said, is a little strong. The overall reduction in breast cancer risk found among the 10,000 participants -- 20 percent -- didn't reach significance from a statistical point of view, he said.
When looked at by subgroups -- those with no previous benign breast disease, those with no prior HRT use, those with no first-degree relative with breast cancer -- the reductions were significant.
"The message is pretty much unchanged by this [new review]," he said, adding "I guess it will get people to look at the data again."
To learn more about HRT, visit the National Library of Medicine.