Ovarian Cancer Risk Doubled by Estrogen-Only HRT

Two decades after the landmark Women’s Health Initiative (WHI) changed the way clinicians thought about hormone therapy and cancer, new findings suggest this national health study is “the gift that keeps on giving.”

Follow-up from two of the WHI’s randomized trials have found that estrogen alone in women with prior hysterectomy significantly increased ovarian cancer incidence and mortality in postmenopausal women. Estrogen and progesterone together, meanwhile, did not increase ovarian cancer risk, and significantly reduced the risk of endometrial cancer. Rowan T. Chlebowski, MD, PhD, of The Lundquist Institute in Torrance, California, presented these results from the latest WHI findings, at the annual meeting of the American Society of Clinical Oncology in Chicago.

Dr Chlebowski and his colleagues conducted an analysis from two randomized, placebo-controlled trials, which between 1993 and 1998 enrolled nearly 28,000 postmenopausal women aged 50-79 years without prior cancer from 40 centers across the United States. (The full WHI effort involved a total cohort of 161,000 patients and included an observational study and two other non-drug trials.)

In one of the hormone therapy trials, 17,000 women with a uterus at baseline were randomized to combined equine estrogen plus medroxyprogesterone acetate, or placebo. In the other trial, about 11,000 women with prior hysterectomy were randomized to daily estrogen alone or placebo. Both trials were stopped early: the estrogen-only trial due to an increased stroke risk, and the combined therapy trial due to findings of increased breast cancer and cardiovascular risk.

Mean exposure to hormone therapy was 5.6 years for the combined therapy trial and 7.2 years for estrogen alone trial.

Ovarian Cancer Incidence Doubles With Estrogen

At 20 years’ follow-up, with mortality information available for nearly the full cohort, Dr Chlebowski and his colleagues could determine that ovarian cancer incidence doubled among women who had taken estrogen alone (hazard ratio [HR], 2.04; 95% CI, 1.14-3.65; P=.01), a difference that reached statistical significance at 12 years’ follow-up. Ovarian cancer mortality was also significantly increased (HR, 2.79; 95% CI, 1.30-5.99; P=.006). Absolute numbers were small, however, with 35 cases of ovarian cancer compared with 17 in the placebo group.

Combined therapy recipients saw no increased risk for ovarian cancer and significantly lower endometrial cancer incidence (106 cases vs 140; HR, 0.72; 95% CI, 0.56-0.92; P=.01).

Conjugated equine estrogen, Dr Chlebowski, said during his presentation at the meeting, “was introduced in US clinical practice in 1943 and used for over half a century, yet the question about hormone therapy’s influence on endometrial and ovarian cancer remains unsettled. Endometrial cancer and ovarian cancer are the fourth and fifth leading causes of cancer deaths in women…and there’s some discordant findings from observational studies.”

Care of Ovarian Cancer Survivors Should Change

The new findings should prompt practice and guideline changes regarding the use of estrogen alone in ovarian cancer survivors, Dr Chlebowski said.

In an interview, oncologist Eleonora Teplinsky, MD, of Valley-Mount Sinai Comprehensive Cancer Care in Paramus, New Jersey, said that apart from this subgroup of ovarian cancer survivors, the findings would not likely have much impact on how clinicians and patients approach hormone replacement therapy today.

“Twenty years ago, the Women’s Health Initiative showed that hormone replacement therapy increases breast cancer risk, and everyone stopped taking HRT. And now people pushing back on it and saying wait a second – it was the estrogen plus progesterone that increased breast cancer, not estrogen alone. And now we’ve got these newer [estrogen] formulations.

“Yes, there’s a little bit of an increased risk [for ovarian cancer]. Patients should be aware. They should know the symptoms of ovarian cancer. But if they have indications and have been recommended HRT, this is not something that we would advise them against because of this very slightly increased risk,” Dr Teplinsky said.

Oncologist Allison Kurian, MD, of Stanford University in Stanford, California, who specializes in breast cancer, also noted that the duration of hormone treatment, treatment timing relative to age of menopause onset, and commonly used estrogen preparations had indeed changed since the time the WHI trials were conducted, making it harder to generalize the findings to current practice. Nonetheless, she argued, they still have real significance.

“WHI is an incredibly complex but also incredibly valuable resource,” said Dr Kurian, who has conducted studies using WHI data. “The first big results came out in 2002, and we’re still learning from it. These are randomized trials, which offer the strongest form of scientific evidence that exists. So whenever we see results from this study, we have to take note of them,” she said.

Because the WHI trials had shown combined therapy, not estrogen alone, to be associated with breast cancer risk, clinicians have felt reassured over the years about using estrogen alone.

“You can’t give it to a person unless they have their uterus removed because we know it will cause uterine cancer if the uterus is in place. But if the uterus is removed, the feeling was that you can give estrogen alone. I think the new piece that is going to get everyone’s attention is this signal for ovarian cancer.”

Something else the new findings show, Dr Kurian said, is that WHI is “the gift that keeps on giving,” even after decades. “Some of the participants had a relatively short-term exposure to HRT. They took a medication for just a little while. But you didn’t see the effects until you followed people 12 years. So we’re now going to be a little more worried about ovarian cancer in this setting than we used to be. And that’s going to be something we’re all going to keep an eye on and think twice about in terms of talking to patients.”

These results help demonstrate what happens when a society invests in science on a national scale, Dr Kurian said. “Here we have a really long-term, incredibly informative study that keeps generating knowledge to help women.”

When the WHI began, it “really was the first time that people decided it was important to systematically study women at midlife. It was a remarkable thing then that society got mobilized to do this, and we’re still seeing the benefits.”

Dr Chlebowski disclosed receiving consulting or advisory fees from Pfizer. Dr Teplinsky and Dr Kurian disclosed no financial conflicts of interest.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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