Hormone replacement therapy (Photo By BSIP/Universal Images Group via Getty Images)
Years after warnings that estrogen therapy could lead to increased cancer risk, a new study has found that it in addition to alleviating hot flashes and other symptoms of menopause, it carries little risk. And even better news: estrogen-only therapy might actually decrease the risk of breast cancer.
Why does this matter? Because about 20 years ago, millions of women stopped taking estrogen, even if it was helping them, because of a report that hormone replacement therapy might increase (not decrease) the risk of breast cancer.
These latest results, published last week in the Journal of the American Medical Association, come from the long-running Women’s Health Initiative, a National Institutes of Health-funded study of more than 160,000 women who were given various hormone therapies and then followed for up to 20 years. The initiative was responsible, somewhat notoriously, for the cancer scare in 2002, when the NIH reported—without consulting many of the scientists leading the study—that hormone replacement therapy increased the risk of breast cancer. This was wrong, as I explained in this column a few years ago, but as a result, many women stopped taking estrogen, and physicians stopped recommending it.
The confusion stemmed from the use of two different types of hormone therapy: estrogen alone or estrogen plus progestin. The increased risk occurred solely in the combination therapy group (estrogen plus progestin), and not in the estrogen-only group. Despite this crucial difference, the Women’s Health Initiative halted the studies of both treatments in 2002, and their press releases didn’t fully explain the difference.
And yet, as Dr. Robert Langer explained in 2017, the WHI trial of estrogen alone (without progestin) continued to track its subjects, and in 2004 that study reported that estrogen-only therapy led to a reduction in breast cancer, and a reduction in coronary heart disease as well.
(Aside: the Women’s Health Initiative website boasts that its 2002 report contains “revolutionary findings about combined hormone therapy,” emphasizing only the harm. I couldn’t find any comparable highlight describing the benefits of estrogen-only therapy.)
The new study, which appeared in JAMA on May 1, confirms several earlier studies that have reported a cancer benefit for estrogen therapy. In addition to its beneficial effects on menopause symptoms (which are widely acknowledged), the new study found that, after an average of 10.7 years, “rates of breast cancer were significantly lower in the CEE group [estrogen only] compared with the placebo group (HR, 0.77).” That HR value means that women who took estrogen had a 23% reduction in their risk of breast cancer.
Further supporting these findings is a 2022 study from NIH, available as a preprint in medRxiv here, which found that women taking estrogen only, compared to no hormones at all, had “significant risk reductions for all study cancers, breast, lung, endometrial, colorectal and ovarian” as well as a 20% reduction in mortality. The 2022 NIH study also found, similarly to the 2002 findings from the Women’s Health Initiative, that when estrogen was combined with progestin, the risk of breast cancer increased.
And there’s more. This 2012 study out of Denmark studied women who received estrogen-only therapy for 10 years starting in the early 1990s. They then followed these women for another 16 years and found that women taking estrogen had a lower risk of heart attack, heart failure or death—and no increased risk of cancer.
(As another aside: the new JAMA paper also reported results on a completely separate study of calcium plus vitamin D. They found that taking supplemental calcium+D didn’t provide any benefit in reducing the risk of bone fractures, confirming what I wrote in a recent column.)
So what’s the bottom line? We now have a raft of evidence showing that for post-menopausal women, estrogen therapy can offer significant benefits not only in treating hot flashes and other “bothersome menopausal symptoms” (to quote JAMA), but also in reducing the risk of some types of cancer. In contrast, hormone replacement therapies that use progestin, which is commonly used in birth control pills, might increase the risk of cancer and should be avoided.
As with most medical treatments, the true picture is complicated, but millions of women today might benefit from estrogen therapy. If you think you might be one of them, talk to your physician.
