Does Postmenopausal Hormone Therapy Cause Breast Cancer

When I recommend menopausal hormone therapy in the clinic, many people first ask back, "Doesn't hormone therapy cause breast cancer?" Ever since a large study was published long ago, this worry has settled in deeply, and quite a few people have hesitated over or stopped treatment because of it. In my clinical experience, the answer to this question is neither "it is unconditionally dangerous" nor "it is completely unrelated." The balance of risk and benefit shifts depending on the type of drug, the duration of use, the age at which you start, and whether or not you still have your uterus. In this article, instead of vague fear, let us look at that balance together based on the evidence.

A large part of the misunderstanding about menopausal hormone therapy stems from a large clinical study published in the early 2000s. As the results were simplified and conveyed through the media at the time, the impression that hormone therapy equals breast cancer took hold.

But that study was conducted in a group with a higher average age, and it used a specific drug combination that is not often used now. As studies re-analyzing the same data continued for more than 20 years afterward, the initial categorical interpretation was considerably refined. In its 2022 position statement, The Menopause Society (formerly NAMS) summarized that the breast cancer risk associated with hormone therapy is small in absolute terms and varies by drug and duration.

As the director, the first thing I check is whether the uterus remains. This is because it is the first fork that determines which drug to use and which way the breast cancer risk tilts.

For those who still have a uterus, using estrogen alone can thicken the endometrium and raise the risk of endometrial cancer, so progestogen (corpus luteum hormone) is used together. Conversely, those who have had a hysterectomy and have no uterus can use estrogen alone. The reason this difference matters is that in several re-analysis studies, the breast cancer signals of the two approaches were different from each other.

In the long-term follow-up analysis of the U.S. Women's Health Initiative (JAMA, 2020), breast cancer occurrence was actually observed to be lower in hysterectomized women who received estrogen-alone therapy, while the combined estrogen-and-progestogen therapy trended toward a somewhat increased risk. In other words, even within the single word "hormone therapy," there are two paths of different texture.

Another axis that governs risk is "how long" and "when you started." Even with the same drug, using it for a short period and using it continuously for over a decade must be viewed differently.

The UK NICE menopause guideline (NG23, 2024 revision) reports that the longer combined therapy is used, the more the breast cancer risk tends to grow gradually. However, this is a cumulative, gradual change, and the additional risk of short-term use is described as being at a very small level. It is also reported that when treatment is stopped, the risk gradually returns toward the background level over time.

The age at start also matters. It is the common view of several societies that during the "window of opportunity" period, when starting shortly after menopause, generally before age 60 or within 10 years of menopause, the balance of benefit versus risk is more favorable. This is why it is good to check in without missing the point when menopausal symptoms begin. If you are curious about what stage your menopausal symptoms are at, you can gauge the timing of starting together through a consultation.

The representative studies dealing with hormone therapy and breast cancer mainly targeted Western women. However, compared with the U.S. and Europe, Korea shows a different pattern in the very frequency of breast cancer occurrence, and there are also differences in average menopausal age and body type distribution.

The Korean Society of Menopause explains that because of these population differences, it is difficult to transfer and apply Western study results directly to Korean women. Also, unlike the past high-dose, fixed-dose approach, recently individualized, low-dose-centered prescriptions are used, which is expected to lower the risk further.

• The study population and the risk background of Korean women are different
• The drug doses and formulations used have changed from the past
• Even the same "hormone therapy" is interpreted differently depending on each person's risk factors

For these reasons, rather than accepting statistical figures directly as your own risk, an interpretation tailored to your own situation is needed.

Another question I often receive in the clinic is about breast cysts. To put the conclusion first, a simple cyst itself is not a contraindication to hormone therapy.

However, when a breast biopsy confirms findings such as atypical hyperplasia or intraductal papilloma, caution is needed, and we decide carefully while consulting with the breast care department. Therefore, there is no need to give up treatment in advance just because you have a cyst; the process of confirming what kind of finding it is comes first.

If you are more curious about the safety and indications of hormone therapy, it helps to refer together to when hormone therapy is needed and the safety of hormone therapy.

Many people ask whether they should get breast screening more often once they start hormone therapy. The heart of the recommendation is to keep up regular screening regardless of whether you are on hormone therapy.

Generally, women aged 40 and older are recommended to have a breast exam once a year. There are also reports that because those on hormone therapy keep up screening more diligently, abnormal findings are detected relatively early. Keeping regular menopausal screening and breast screening together becomes the foundation for continuing treatment with peace of mind.

Overall health management after menopause is also a matter of looking after not only hormones but bone density, metabolism, and vascular health together. If needed, you can have a comprehensive check at the level of a menopausal hormone clinic.

The relationship between menopausal hormone therapy and breast cancer cannot be answered with the dichotomy of "dangerous/safe." It must be weighed by weighing together the presence of the uterus, the type of drug, the duration of use, the age at start, and the individual's risk factors.

We do not recommend either putting off treatment because of vague fear even when quality of life is declining due to symptoms, or starting recklessly without examining the risk factors. In my clinical experience, the safest path is to decide together with a specialist by weighing your benefits and risks concretely. If you are hesitant, please feel free to consult comfortably about your questions on hormone therapy, and I recommend finding the choice that fits you together.

In the next installment, I will continue by covering how we judge hormone therapy when there is a breast cancer patient in the family.

Written by: Lee Dong-hee Director · OB-GYN specialist · View doctor profile

First published March 3, 2022 · Last reviewed May 30, 2026

References: The Menopause Society (NAMS) Hormone Therapy Position Statement (2022), NICE Menopause Guideline NG23 (2024), Women's Health Initiative Long-term Follow-up, JAMA (2020), Korean Society of Menopause guidebook for menopausal women

This article is intended to provide general health information and does not replace individual diagnosis or treatment. If you have symptoms, please consult through a medical visit.