Menopause Hormone Therapy May Rise Breast Cancer Risk

A new study found that starting hormone therapy at around the time of menopause is associated with a higher risk of breast cancer, compared to starting it later.

There is a lot of controversy about menopause and hormone-replacement therapy, whether or not the medication should be followed, and if so, when's the best time to do it – before, during or after menopause.

Many studies have concluded that the users of hormonal therapy have an increased breast cancer incidence, especially women who take an estrogen-progestin mix, compared to those who take estrogen alone.

But not so much research has been conducted on the timing of hormone therapy as a risk factor, except for two previous studies, suggesting that the time between menopause and the beginning of hormone therapy could have an influence of breast cancer risks, but only in certain subgroups.

To obtain more information on this, Valerie Beral, FRS, of Oxford University and colleagues, used data from the Million Women Study (MWS) in the UK.

They estimated the risks of breast cancer between hormone therapy users and past users, compared to non-users, in a total of 1.3 million women.

They also accounted for the different types of hormone therapy.

Their findings concluded that women starting hormone therapy at the time of menopause were at greater risk of breast cancer than those who waited a while before doing so.

“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 authors write.

This very large research concluded that women who started hormone therapy five years or more after menopause had little or no higher breast cancer risk, regardless of the type of hormone therapy used, how long they used it, and whether they were overweight or obese.

“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.”

Rowan T. Chlebowski, MD, PhD, of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center and Garnet Anderson from the Fred Hutchinson Cancer Research Center, write in an accompanying editorial, that this study confirms similar findings from the Women's Health Initiative (WHI) in the US.

They add that since the patterns of breast cancer risks in the two studies are so similar, even if the methods used were quite different, the veracity of the results is very high.

The study was published online in The Journal of the National Cancer Institute.