Duavee and Breast Health: What the Research Actually Shows

For two decades, fear of breast cancer has kept many women from treating hot flashes, night sweats and bone loss with hormone therapy. The research tells a more nuanced story, and one medication, Duavee, sits right at the center of it.

What is Duavee?

Duavee is a once-daily tablet approved by the FDA in 2013 for two uses in postmenopausal women who still have a uterus: treating moderate-to-severe hot flashes and preventing postmenopausal osteoporosis.¹

It combines two ingredients:

• Conjugated estrogens 0.45 mg, the same estrogen found in Premarin
• Bazedoxifene 20 mg, a selective estrogen receptor modulator, or SERM

What makes Duavee different is what it doesn't contain: a progestin. Women with a uterus who take estrogen normally need a progestin to protect the uterine lining. Duavee uses bazedoxifene for that job instead.

Why the progestin question matters

The Women's Health Initiative (WHI) is the largest randomized trial of hormone therapy, and it is the source of most fear about hormones and breast cancer. In 2002, headlines reported a 26% increase in breast cancer among women taking estrogen plus a progestin.²

Long-term follow up revealed something else often missed in headlines. Women taking conjugated estrogen alone after hysterectomy had about 22% fewer breast cancers and about 40% fewer breast cancer deaths than placebo.³

That small increase appears tied to the progestin, not the estrogen. The problem is that women with a uterus can't simply drop the progestin, because unopposed estrogen raises the risk of endometrial cancer. Duavee was designed to solve exactly that problem.

How a SERM protects the uterus and breast

Think of the estrogen receptor as a light switch. Estrogen flips it on. A SERM binds the same switch but changes its shape, and each tissue reads that new shape differently depending on which helper proteins it has.

Laboratory research has mapped two ways this blocking happens in uterine and breast cells.⁴

• Repressors instead of activators: on the combination, the estrogen receptor pulls in proteins that switch growth genes off.
• Receptor breakdown: the combination tags estrogen receptor alpha for destruction in uterine and breast cells, but not in bone cells.

Bazedoxifene alone also degrades the estrogen receptor in breast cancer cells, much like fulvestrant, a drug used to treat breast cancer. That is why researchers describe it as part SERM and part SERD (selective estrogen receptor degrader).^5,6

What the clinical trials show

Duavee was studied in the SMART (Selective estrogens, Menopause, And Response to Therapy) trials. This phase 3 program enrolled about 7,500 postmenopausal women.

Hot flashes

By week 12, moderate-to-severe hot flashes fell 74% on Duavee, compared with 51% on placebo.⁷

Bone

Lumbar spine and hip bone density increased on Duavee and decreased on placebo.⁸ One caveat: the trials measured bone density, not fracture rates.

Uterus

Endometrial hyperplasia stayed below 1% over two years, similar to placebo.⁹ Bleeding and spotting rates also tracked closely with placebo¹⁰ and were far lower than with standard estrogen plus progestin.⁸

Breast

• Breast density: density didn't change over 1 year in SMART-5, matching placebo. Estrogen plus progestin was the only group where it rose.¹¹ A separate trial found no significant change over 2 years.¹²
• Breast tenderness: rates were similar to placebo and lower than with estrogen plus progestin.⁸
• Breast cancer: overall cancer rates, including breast cancer, were low and similar to placebo.¹³

What about women at higher risk, or with early breast cancer?

Women at higher risk who have not had breast cancer

Many women at elevated risk avoid tamoxifen or aromatase inhibitors because those drugs can worsen hot flashes. That raised a question at the University of Kansas: could Duavee relieve symptoms while also improving markers of breast risk?

In a 6-month pilot study, 28 women at increased risk took Duavee.¹⁴ The researchers found:

• Lower breast density, measured as fibroglandular volume
• Lower Ki-67, a marker of breast cell growth, in women whose baseline levels were higher
• Median hot flash scores that dropped from 15 to 0, plus better quality-of-life scores

Those results led to an NCI-funded, randomized Phase IIB trial at six U.S. centers (NCT04821141). Enrollment has closed, and results are still pending.¹⁵

Women with DCIS (early, non-invasive breast cancer)

The PROMISE trial at Northwestern University asked a bolder question: is Duavee safe for women who already have ductal carcinoma in situ (DCIS), an early, non-invasive form of breast cancer? In this phase 2 trial, 141 postmenopausal women with estrogen receptor-positive DCIS were randomized to Duavee or placebo for 4 weeks between diagnosis and surgery, and 117 completed the study.¹⁶

Duavee lowered Ki-67, a marker of breast cell growth, significantly more than placebo. Hot flashes improved, quality of life did not worsen, and no serious treatment-related side effects were reported.

These results were presented as an abstract at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting and have not yet been published as a full peer-reviewed paper. Four weeks of treatment also can't tell us anything about recurrence or long-term safety.

The honest caveats

• Short trials: the studies ran from 4 weeks to 2 years and weren't designed to measure long-term breast cancer outcomes.
• Biomarkers, not outcomes: the high-risk and DCIS studies measured markers like Ki-67 and breast density. They haven't shown fewer cancers or recurrences. The high-risk pilot also excluded BRCA carriers and women with prior LCIS.
• Not a prevention drug: Duavee is not FDA approved for breast cancer prevention or treatment.
• FDA warnings still apply: like other systemic estrogens, Duavee carries a boxed warning for endometrial cancer, cardiovascular disorders (including blood clots and stroke) and probable dementia in women 65 and older.
• Who shouldn't take it: women with a history of breast cancer, blood clots, stroke, heart attack, liver disease or unexplained vaginal bleeding, among others, and women taking other estrogens or progestins.
• Funding: the SMART trials were sponsored by the manufacturer, Wyeth/Pfizer.

Who might consider Duavee?

Duavee isn't the right fit for everyone, but it is worth discussing if you:

• Still have a uterus and have moderate-to-severe hot flashes or night sweats
• Have low bone density or risk factors for osteoporosis
• Have tried a progestin and struggled with bloating, breast tenderness, mood changes or breakthrough bleeding
• Have dense breasts, or a family history that makes you uneasy about standard estrogen plus progestin

It may be a less natural fit if you strongly prefer bioidentical estradiol, need help mainly with vaginal dryness (local vaginal estrogen is often the simpler choice), or want a non-oral option such as a patch, which avoids the liver's first-pass effect. These trade-offs are exactly why hormone decisions should be individualized rather than one-size-fits-all.

The bottom line

Duavee offers a progestin-free option for women with a uterus. It relieves hot flashes, protects bone, keeps the uterine lining quiet, and so far looks neutral to favorable for the breast. Early research in higher-risk women and in women with DCIS is encouraging but not yet definitive. For women with significant symptoms who worry about breast risk, it deserves a place in the conversation. Your personal and family history, your preferences about bioidentical hormones, and your goals should guide the choice.

References

1. Duavee (conjugated estrogens/bazedoxifene) Prescribing Information. Pfizer; current label.
2. Rossouw JE, Anderson GL, Prentice RL, et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA. 2002;288(3):321–333.
3. Chlebowski RT, et al. Association of menopausal hormone therapy with breast cancer incidence and mortality during long-term follow up of the Women's Health Initiative randomized clinical trials. JAMA. 2020;324(4):369–380.
4. Han SJ, Begum K, Foulds CE, et al. The dual estrogen receptor α inhibitory effects of the tissue-selective estrogen complex for endometrial and breast safety. Mol Pharmacol. 2016;89(1):14–26.
5. Lewis-Wambi JS, Kim H, Curpan R, et al. The selective estrogen receptor modulator bazedoxifene inhibits hormone-independent breast cancer cell growth and down-regulates estrogen receptor α and cyclin D1. Mol Pharmacol. 2011;80(4):610–620.
6. Fanning SW, Jeselsohn R, Dharmarajan V, et al. The SERM/SERD bazedoxifene disrupts ESR1 helix 12 to overcome acquired hormone resistance in breast cancer cells. eLife. 2018;7:e37161.
7. Pinkerton JV, Utian WH, Constantine GD, et al. Relief of vasomotor symptoms with the tissue-selective estrogen complex containing bazedoxifene/conjugated estrogens: a randomized, controlled trial. Menopause. 2009;16(6):1116–1124.
8. Pinkerton JV, Harvey JA, Lindsay R, et al. Effects of bazedoxifene/conjugated estrogens on the endometrium and bone: a randomized trial. J Clin Endocrinol Metab. 2014;99(2):E189–E198.
9. Pickar JH, Yeh IT, Bachmann G, Speroff L. Endometrial effects of a tissue selective estrogen complex containing bazedoxifene/conjugated estrogens as a menopausal therapy. Fertil Steril. 2009;92(3):1018–1024.
10. Archer DF, Lewis V, Carr BR, et al. Bazedoxifene/conjugated estrogens (BZA/CE): incidence of uterine bleeding in postmenopausal women. Fertil Steril. 2009;92(3):1039–1044.
11. Pinkerton JV, Harvey JA, Pan K, et al. Breast effects of bazedoxifene-conjugated estrogens: a randomized controlled trial. Obstet Gynecol. 2013;121(5):959–968.
12. Harvey JA, Pinkerton JV, Baracat EC, et al. Breast density changes in a randomized controlled trial evaluating bazedoxifene/conjugated estrogens. Menopause. 2013;20(2):138–145.
13. Mirkin S, Pickar JH. Management of osteoporosis and menopausal symptoms: focus on bazedoxifene/conjugated estrogen combination. Int J Womens Health. 2013;5:465–475.
14. Fabian CJ, Nye L, Powers KR, et al. Effect of bazedoxifene and conjugated estrogen (Duavee) on breast cancer risk biomarkers in high-risk women: a pilot study. Cancer Prev Res. 2019;12(10):711–720.
15. Randomized IIB study of bazedoxifene plus conjugated estrogens on breast imaging and tissue biomarkers in women at increased risk for breast cancer. ClinicalTrials.gov NCT04821141.
16. Kulkarni S, et al. The PROMISE study: a presurgical randomized clinical trial of CE/BZA vs placebo in postmenopausal women with ductal carcinoma in situ. J Clin Oncol. 2025;43(16 suppl):512 (ASCO Annual Meeting abstract). ClinicalTrials.gov NCT04821141 is a separate trial; PROMISE is NCT02694809.

This article is for educational purposes and is not a substitute for individualized medical advice. Talk with your healthcare provider before starting or changing any medication.