MHT and cancer risk, in real numbers.

Current NICE guidance says the increase with combined MHT rises with duration and can persist for at least 10 years after stopping. Sequential combined MHT has a lower risk than continuous combined treatment, but a higher risk than no MHT. This applies to people without a personal history of breast cancer.

The WHI randomized trials tested specific formulations. In the 2020 long-term follow-up, conjugated equine estrogen alone in participants with a prior hysterectomy was associated with lower breast cancer incidence and mortality; combined conjugated equine estrogen plus medroxyprogesterone acetate increased incidence. Those results can't be extended to every estrogen product or used as a reason to prescribe HRT to prevent breast cancer.

A 2024 Norwegian cohort of 1,275,783 women still found associations with systemic oral and transdermal HRT, varying by formulation. A patch can have a lower blood-clot risk than a tablet without eliminating breast cancer risk. This was observational research, not proof of causation. The article was corrected in August 2025 without changing its overall conclusions.

Some observational studies suggest differences between progestogens. But NICE says evidence is insufficient to establish a lower breast cancer risk with micronized progesterone or dydrogesterone. The BMJ 2020 study assessed dydrogesterone, not micronized progesterone; it can't support a micronized-progesterone risk estimate.

This is the cleanest of the cancer-risk conversations. Unopposed estrogen (estrogen without progesterone) thickens the uterine lining and significantly raises endometrial cancer risk. The whole reason combined MHT exists is to prevent that. If you have a uterus and you're on estrogen, you need adequate progesterone (or a Mirena IUS, which delivers it locally). If you don't have a uterus, this concern doesn't apply to you.

The signal here is real but small, and seen across both combined and estrogen-only MHT in observational data. The Collaborative Group's 52-study reanalysis (Lancet 2015) put the absolute increase at roughly 1 extra ovarian cancer per 1,000 women using MHT for 5 years from age 50, and about 1 extra death per 1,700. The signal fades after stopping, but for people who used MHT for five years or more, a small increase is still measurable about ten years later.

For women with a strong family history or a BRCA1/2 variant — and especially after risk-reducing salpingo-oophorectomy, where MHT is often actively recommended up to the natural age of menopause — this decision belongs with your oncology or genetics team specifically, not with a website. UK and US guidance broadly supports MHT after risk-reducing surgery because the risks of premature surgical menopause are substantial, but your individual risk profile has to be weighed first.

One of the underreported parts of the WHI: combined MHT reduced colorectal cancer incidence in the trial. The mechanism isn't fully understood. This isn't a reason to start HRT for colorectal protection (screening is what does that work), but it's part of the honest accounting when people only quote the breast cancer side of the ledger.

Cervical cancer is overwhelmingly HPV-driven. MHT use doesn't change that. Continue cervical screening on your country's normal schedule regardless of whether you're on MHT.

Some early signals around MHT and lung cancer mortality in smokers haven't held up consistently. The lung cancer risk that matters is smoking history. If you smoke, the smoking conversation is the bigger one by orders of magnitude.

A 2025 AJOG review of eight observational studies found no overall increase in recurrence or mortality with vaginal estrogen. Its pooled estimates were unadjusted, so it can't prove that treatment is risk-free or protective. A JAMA Oncology study in the January 2024 issue followed 49,237 women and found no higher early breast cancer-specific mortality; it didn't measure recurrence.

The Danish 2022 study found an increased recurrence association in the subgroup using vaginal estrogen alongside aromatase inhibitors. Newer reassuring overall findings don't settle that question. NICE still describes uncertainty after estrogen receptor-positive cancer and recommends identifying options with a breast cancer specialist during aromatase inhibitor treatment.

Start with non-hormonal vaginal moisturizers and lubricants. If symptoms persist, discuss whether local estrogen suits your cancer type, recurrence risk and current treatment. Vaginal DHEA is hormonal, not a non-hormonal moisturizer. NICE's interventional procedures guidance says vaginal laser should only be used in the context of research. Regulatory label changes aren't evidence that systemic MHT is suitable after hormone-sensitive cancer.