Can Hormones be Used After Breast Cancer? What the Data Shows

You reach the end of your breast cancer treatment road and then, in menopause, you find yourself facing another possible dilemma. Many breast cancer survivors reach menopause facing a new kind of challenge: intense hot flashes, night sweats, sleep loss, and painful intimacy. Most are told hormone therapy is off-limits because of fears it could cause the cancer to return.

But current research tells a different story. Over the past 25 years, about two dozen studies have explored whether hormone therapy increases the risk of recurrence or death in women who have had breast cancer. With one exception, they have not found evidence of harm.

What We’ve Learned from the Research

The idea that hormone therapy increases recurrence risk largely stems from one early study called HABITS (Hormonal Replacement Therapy After Breast Cancer—Is It Safe?). Conducted in Sweden, HABITS was stopped early after finding more recurrences among women on hormone therapy. However, later analysis revealed important flaws.

Women in HABITS were more likely to have received combined estrogen and synthetic progestins, while those in the parallel Stockholm trial were given different regimens and followed more closely. When the Stockholm study results were published, there was no increase in recurrence among hormone users.

Long-term pooled follow-up of both studies later concluded that data were too limited for firm conclusions and that the HABITS findings likely reflected differences in hormone formulations and study design, not an inherent danger of estrogen therapy itself.

Does Tumor Type Matter?

Yes, and it’s an important distinction. The potential risk from hormone therapy depends largely on whether a woman’s original tumor was estrogen receptor–positive (ER+) or triple-negative (ER-, PR-, HER2-).

Women with ER+ tumors have cancers that respond to estrogen, so the concern about hormone therapy stimulating residual cancer cells is mostly theoretical but understandable. Even so, multiple modern studies have shown no increase in recurrence or mortality for women with ER+ disease who used systemic hormone therapy after treatment. Caution and careful monitoring are still advised, but it is not considered automatically unsafe.

Women with triple-negative breast cancer (TNBC), on the other hand, have tumors that do not respond to estrogen or progesterone. Because these cancers lack hormone receptors, estrogen therapy has no biological target to act on. For these women, there is no evidence that hormone therapy increases recurrence risk, and many experts consider it an acceptable option after treatment, especially when quality of life is severely affected.

In short, risk varies by tumor biology, but across all subtypes, the data remain reassuring. The majority of studies show no increase in recurrence or mortality from appropriately used hormone therapy after breast cancer.

Modern Evidence Paints a Reassuring Picture

Recent cohort studies and reviews continue to show that hormone therapy, when used appropriately, does not raise the risk of breast cancer recurrence or death.

A large Danish national cohort of more than 8,000 breast cancer survivors found no increase in recurrence or mortality among women who used systemic menopausal hormone therapy or vaginal estrogen therapy after treatment.

A 2025 review published in Menopause reached similar conclusions: across roughly 25 studies, there is no convincing evidence that hormone replacement therapy after breast cancer increases recurrence or overall mortality. The authors emphasized that prior fears have not been supported by data and that women deserve individualized, evidence-based discussions rather than blanket prohibitions.