Hormone replacement therapy safer taken after menopause
Hormone replacement therapy may be safer for women when started further away from menopause.
Researchers found waiting five years to begin menopausal hormone replacement therapy can lower the chances of breast cancer, regardless of which type of hormones are used.
Studies show combination hormones using estrogen and progesterone are riskier for breast cancer development, compared to estrogen, but scientists say few studies have looked at the association between health risks and when a woman starts taking hormones.
Valerie Beral, FRS, of Oxford University and colleagues, used data from the Million Women Study (MWS) in the UK to find less risk of breast cancer from later hormone therapy initiation. Women who begin replacing estrogen and progesterone around the time of menopause were at greater risk for breast cancer.
The researchers estimated the estimated adjusted risk of breast cancer among hormone therapy users and past users and compared the data to non-users - 1.13 million women were included in the study.
The new finding follows two previous studies that suggested hormone therapy taken further from menopause was less risky for breast cancer, but only in certain subgroups.
Beral says, "In this large study, we found greater risks of breast cancer if hormonal therapy use began either before or soon after menopause than after a longer gap; and this pattern of risk was seen across different types of hormonal therapy, among women who used hormonal therapy for either short of long durations, and also in lean and in overweight and obese women."
Two other researchers commenting on the study, Rowan T. Chlebowski, M.D., Ph.D., of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center and Garnet Anderson from the Fred Hutchinson Cancer Research Center supported the findings, pointing to the similarity found from the Women's Health Initiative (WHI) in the U.S.
They also note discrepancies in hormone therapy studies - the WHI study did not find the same risk of breast cancer with estrogen therapy, while the Million Women Study (MWS) in the UK found a significantly increased risk of cancer. The question of whether estrogen only hormone replacement therapy is riskier for breast cancer remains unanswered.
The study, published in the Journal of the National Cancer Institute, suggests lower breast cancer risk for women from starting hormone therapy further from menopause. In the analysis, the chances of developing the disease were significantly lower for women beginning estrogen alone, or estrogen and progesterone, 5 years or more after menopause.
JNCI J Natl Cancer Inst (2011): doi: 10.1093/jnci/djq527
"Breast Cancer Risk in Relation to the Interval Between Menopause and Starting Hormone Therapy"