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."
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