Starting hormone replacement therapy near the time menopausal symptoms begin may be linked to a higher risk of breast cancer compared with starting later, a new British study suggests.
Past studies have shown that breast cancer cases are higher among women who've taken hormone replacement therapy. Researchers are still trying to pin down specifics, such as how timing of hormone therapy may make a difference.
The study in Friday's online issue of The Journal of the National Cancer Institute offers a glimpse into that still murky question.
Valerie Beral of Oxford University and her colleagues used data from the Million Women Study in the U.K. to compare breast cancer risks of current and past users of HRT. The average age of participants when the study began was 57.
Investigators wanted to analyze any differences between women taking the estrogen-progestin combination form of HRT and estrogen alone from May 1996 to December 2001.
Among women on estrogen-only HRT at the time period studied, there was little or no increase in breast cancer risk if the treatment was started five years or more after menopause, Beral's team said.
But women showed 1.43 times the risk if they started HRT before or less than five years after menopause — an increased risk the researchers called statistically significant.
"A new finding of this study, which has been little investigated previously, is that the interval between menopause and starting hormonal therapy has a substantial effect on breast cancer risk," the study's authors wrote.
The investigators saw the same pattern of risk in relation to menopause timing for different types of HRT and regardless of weight.
A journal editorial accompanying the study noted its similarities to the large Women's Health Initiative study, which lends supports to the validity of the findings, said editorial authors Dr. Rowan Chlebowski of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center and Garnet Anderson from the Fred Hutchinson Cancer Research Center.
Data from both the Million Women Study and the U.S. Women's Health Initiative are being analyzed to reveal more about the heart, stroke and cancer risks for postmenopausal women.