Does Duavee Lower Breast Cancer Risk? What We Know So Far

Every so often a patient sends me a link with a version of this question:

"I just read that Duavee might lower breast cancer risk. Is this the menopause medication I should be taking?"

It's a reasonable thing to ask. Hot flashes are miserable, breast cancer is frightening, and one pill that helped with both would get anyone's attention.

There's a real reason people are talking about it, too. Duavee, which combines conjugated estrogens with bazedoxifene, has been around for years as a treatment for hot flashes and for prevention of bone loss. Researchers have started asking whether it may have different effects on breast tissue than conventional estrogen-plus-progestin therapy.

So far, the research is encouraging, but it is still early. It's an interesting question. We have some early clues, but we don't have an answer yet.

What Is Duavee, and Why Is It Interesting?

Duavee is conjugated estrogens plus bazedoxifene. The estrogen takes care of the hot flashes. Bazedoxifene is a selective estrogen receptor modulator, or SERM, which sounds technical but just means it acts differently in different tissues. In the uterus, it blocks estrogen's stimulating effect on the lining, which is why a woman who still has her uterus can take Duavee without a progestogen.

That tissue-selective behavior is also what makes it interesting for the breast. The hope is that you could get estrogen's benefits for symptoms and bone without some of the breast effects people worry about with estrogen plus progestin. It's a reasonable hypothesis, and a hypothesis isn't an answer.

Duavee is FDA-approved for moderate to severe hot flashes and for prevention of postmenopausal osteoporosis in women with a uterus. It isn't approved to prevent breast cancer.

What Did the PROMISE Study Find About Breast Cancer Risk?

The recent attention comes from a study called PROMISE presented at the 2025 American Society of Clinical Oncology annual meeting and published as a conference abstract. A full peer-reviewed report of the trial results does not appear to be available yet.

It was a multicenter, randomized, double-blind, placebo-controlled trial that enrolled postmenopausal women with newly diagnosed, estrogen receptor-positive DCIS who took Duavee or placebo for about four weeks before surgery. DCIS is noninvasive, but it is still breast cancer, often called stage 0 breast cancer. Researchers looked at Ki-67, a marker of how actively breast cells are dividing.

On average, Ki-67 fell by about 5.6 percentage points with Duavee, compared with about 1.1 percentage points with placebo. The difference between the two groups was statistically significant. That's encouraging because it suggests that Duavee reduced breast-cell proliferation during the short treatment period. The researchers concluded that the findings provide supportive evidence that Duavee may reduce the risk of developing invasive breast cancer.

But there's an important distinction: the study did not actually measure whether women went on to develop fewer invasive breast cancers. Ki-67 is a biomarker, so this trial gives us a clue about what Duavee may be doing in breast tissue. It doesn't establish that taking Duavee prevents breast cancer over the long term.

What Do the Other Duavee Studies Show?

PROMISE isn't the first study to suggest that Duavee may have favorable effects in the breast. An earlier small study in peri- and postmenopausal women at increased breast cancer risk found improvements in hot flashes and some encouraging changes in breast tissue, including lower Ki-67 in women with higher levels to begin with. Mammograms also showed less fibroglandular breast tissue. The study was small and didn't have a placebo group, so it couldn't tell us whether Duavee prevents breast cancer. It did, however, provide a reason to keep studying the question.

A 2023 observational study looked at insurance-claims data from women starting Duavee or estrogen plus progestin. Breast cancer rates were lower among women taking Duavee, but the difference was not statistically significant. The study had several important limitations, including relatively short follow-up, different hormone regimens in the comparison group, and no comparison with women taking no hormone therapy. It was also funded by Pfizer, the maker of Duavee.

Taken together, these studies are encouraging, but they don't establish that Duavee lowers breast cancer risk.

What Does This Mean If You’re Worried About Breast Cancer?

If you're a good candidate, Duavee can be a perfectly reasonable option to discuss for hot flashes, and it may be useful when osteoporosis prevention is also on the table.

I wouldn't pick Duavee because you believe it's been proven to prevent breast cancer. It hasn't. If you have DCIS, invasive breast cancer, or a history of either, PROMISE does not make Duavee a routine option for hot flashes. The prescribing information lists "known, suspected, or past history of breast cancer" as a contraindication and says that Duavee's effect on breast-cancer risk is unknown.

That can feel counterintuitive after reading about the trial. But the women in PROMISE took the medication for a short, closely monitored stretch before surgery, which is very different from long-term systemic hormone therapy after a diagnosis.

The Bottom Line

Duavee relieves hot flashes, can be useful for osteoporosis prevention, and small studies show encouraging changes in breast-tissue biomarkers. PROMISE adds another piece of evidence suggesting that Duavee may have favorable effects on breast-cell proliferation, at least over the short term in the women studied.

That's enough to make the question worth studying. It is not enough to call Duavee a breast-cancer-prevention drug.

For now, I think of it as a menopause treatment with a genuinely interesting breast-research story.

If you're weighing hormone therapy, bring the full picture to your visit: your symptoms, whether you have a uterus, your bone health, your personal and family breast history, and your cardiovascular and clotting risk. Those things will point you toward the right treatment far better than a headline will.