Does hormone replacement therapy increase the risk of cancer?

The question every woman considering HRT asks, and the answer that's more reassuring than the headlines suggest

If you've hesitated over starting HRT because of cancer risk, you're not being irrational. You're responding to over twenty years of headlines that started with one enormous study and never quite caught up with everything that came after it.

Where the fear started

In 2002, the Women's Health Initiative, a huge American study, reported that women taking combined HRT (oestrogen and progestogen) had a higher risk of breast cancer, heart disease and stroke. The findings made front pages worldwide. HRT prescriptions collapsed almost overnight, and for many women and many doctors, the word HRT became shorthand for danger.

The trouble is, the full picture was more complicated than the headlines allowed, and most of that complexity emerged years later, well after the fear had already taken hold. The women in the original study were, on average, considerably older than the typical woman starting HRT today, many well over a decade past menopause, which later turned out to matter a great deal.

What we now know

It depends on the type. Combined HRT, oestrogen plus progestogen, carries a small increase in breast cancer risk with long term use. Oestrogen-only HRT, typically used by women who've had a hysterectomy, does not carry the same risk, and some research suggests it may even be linked to a lower risk of breast cancer.

It depends on timing. Starting HRT around the time of menopause, rather than a decade or more afterwards, appears to carry less risk and may bring added benefits for heart and bone health. This is often called the timing hypothesis and it's one of the clearest developments since the original 2002 study.

It depends on how you measure risk. This is the part most reporting leaves out. The increased risk reported in 2002 was a relative risk, not an absolute one. In real terms, for women on combined HRT, that works out to a small number of additional cases per thousand women over several years, comparable to or smaller than the increased risk linked to drinking two or more units of alcohol daily, or to being overweight. None of that makes the risk meaningless. It does make it worth putting in proportion.

It isn't only about breast cancer. HRT's relationship with cancer risk isn't uniform across cancer types. Oestrogen-only HRT has been linked to a small increase in endometrial cancer risk in women who still have a womb, which is why it's typically combined with progestogen for those women. On the other side, HRT use has been associated with a reduced risk of bowel cancer.

It's personal. Family history, existing health conditions, lifestyle and the severity of your menopause symptoms all factor into whether HRT makes sense for you. This is precisely why the conversation belongs with your GP, not with a headline from two decades ago.

Understanding relative risk versus absolute risk

This distinction deserves its own explanation because it is so often the source of confusion. A relative risk increase of, say, thirty per cent sounds alarming in isolation. But if the underlying absolute risk is small to begin with, a thirty per cent relative increase might mean only a handful of additional cases across every thousand women, rather than a dramatic jump in real terms. News coverage of medical studies almost always reports the relative figure, since it sounds more significant, while the absolute figure is the one that actually helps an individual woman weigh her own decision.

Putting this in everyday context helps. The increased breast cancer risk associated with several years of combined HRT use is, in absolute terms, similar in scale to the increased risk associated with being moderately overweight, or with drinking regularly at levels many people would not consider excessive. None of these risks are zero, and none of them are reasons to panic, which is exactly the balance that got lost in 2002 and has taken two decades to partially recover.

What the more recent research adds

Since 2002, larger and more carefully designed studies, along with long term follow up of the original participants, have refined the picture considerably. Later analysis found that much of the original increased risk applied specifically to combined HRT started later in life, rather than to HRT use broadly. Studies looking specifically at younger, recently menopausal women starting HRT have generally found a more favourable risk picture, alongside genuine benefits for bone density, cardiovascular health and quality of life during the menopause transition.

This does not mean risk has disappeared. It means the conversation has become more precise, moving from a blanket verdict on HRT as a category towards a more individualised assessment based on type, timing, dose and personal risk factors, which is exactly how a good GP consultation on this topic should feel today.

The bottom line

Most UK and international menopause specialists now regard HRT as a safe, often life improving option for the majority of women, when prescribed appropriately and reviewed regularly. The 2002 study wasn't wrong so much as incomplete, and the fear it created has outlived the nuance that followed it.

If cancer risk is what's holding you back from a conversation about HRT, that conversation, not avoidance, is the way to actually resolve it. Your GP can talk you through your personal risk profile rather than a two decade old headline.

Frequently asked questions

Does HRT cause cancer? HRT does not act as a straightforward cause of cancer in the way that phrase implies. Certain types and durations of HRT are associated with a small increase in the risk of specific cancers, while other types carry no such increase or are linked to a reduced risk of other cancers. It is a nuanced picture rather than a single yes or no answer.

How long can I safely stay on HRT? There is no fixed time limit that applies to every woman. Many specialists now support continuing HRT for as long as the benefits outweigh the risks for that individual, reviewed regularly with a GP, rather than applying an automatic cut off at a set number of years.

Should I avoid HRT if cancer runs in my family? Not necessarily, but it is an important factor to raise with your GP, who can weigh your specific family history against the type of HRT being considered and may suggest particular monitoring or a different formulation.

How different types of HRT are typically prescribed

Understanding the main categories helps make sense of why risk varies so much between them. Oestrogen-only HRT is generally prescribed for women who have had a hysterectomy, since there is no womb lining to protect and therefore no need for progestogen. Combined HRT, oestrogen alongside progestogen, is prescribed for women who still have a womb, since progestogen protects the uterine lining from the effects of oestrogen alone. Within combined HRT, there is a further distinction between cyclical regimens, which produce a monthly bleed and are typically used earlier in perimenopause, and continuous combined regimens, which do not, and are generally used once a woman is further past her final period.

Delivery method also varies and can affect risk profile. Oestrogen delivered through the skin, via a patch, gel or spray, is generally considered to carry a lower risk of blood clots than oestrogen taken as a tablet, since it bypasses the liver in a way that oral forms do not. This is one of several reasons a GP may recommend a particular formulation over another based on your personal risk factors, rather than defaulting to whichever type is most commonly prescribed.

Questions worth bringing to your GP appointment

A short list of specific questions tends to make HRT consultations considerably more useful than a general request to “discuss my options”:

• Given my personal and family history, which type of HRT would you recommend and why

• What is my absolute risk increase, not just the relative risk, with this specific option

• Would a different delivery method, such as a patch rather than a tablet, change my risk profile

• How often should we review this once I start

• What symptoms would mean I should come back sooner than my scheduled review

Walking in with these questions tends to produce a far more tailored conversation than simply asking whether HRT is safe, since safety here is genuinely relative to the individual rather than a single fixed answer.

Why the fear outlasted the evidence

There is a well known pattern in health reporting where an alarming initial finding travels much further and faster than the more reassuring correction that follows it years later. The 2002 study made global front pages. The subsequent, more nuanced follow up studies, published gradually over the following decade, received a fraction of that coverage, largely confined to medical journals and specialist press rather than national news. The result is a generation of women, and in some cases their doctors, whose understanding of HRT risk froze at the 2002 headline rather than updating alongside the evidence.

This is worth naming plainly, because it means the caution many women feel is not a personal failing or excessive worry. It is a reasonable response to information that was, for a long time, incomplete, and that has taken years longer to correct in public understanding than it did in the research itself.

References

NHS - www.nhs.uk

British Menopause Society - www.thebms.org.uk

Cancer Research UK - www.cancerresearchuk.org

Royal College of Obstetricians and Gynaecologists - www.rcog.org.uk

Mayo Clinic - www.mayoclinic.org