What you've heard
Hormone therapy causes breast cancer
Verdict
Partly true and badly overstated
Partly true and badly overstated. The risk is real, modest and depends on type and duration. It argues for a careful choice of treatment; it does not argue for refusing one.
Does hormone therapy cause breast cancer?
Partly true and badly overstated. The risk is real, modest and depends on type and duration. It argues for a careful choice of treatment; it does not argue for refusing one.
The type matters more than the headline. In the Women's Health Initiative, combined estrogen and progestin raised breast cancer modestly, while estrogen alone went the other way: fewer breast cancers and fewer breast cancer deaths over two decades of follow-up. The largest pooled analysis of observational data gives the size of the risk. Of 1,000 women who take hormones for five years from age fifty, it estimates about 20 extra breast cancers on estrogen plus a daily progestogen, about 14 when the progestogen is taken part of each month, and about 5 on estrogen alone. Ten years roughly doubles these. Vaginal estrogen showed no excess, and some of the excess lasted years after stopping.35
Where the book tests it
What the book recommends instead
In the reproductive years, track your cycle as a vital sign
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.for spotting problems earlythe wider vital-sign idea is expert opinionHow: note the first day of each period, how long it lasts and how heavy it is, in any calendar or app, and watch for change from your own pattern. Why: the cycle reports on energy, iron loss, hormones and, later, the start of the transition, for free.
In perimenopause, take your symptoms to a clinician, because effective treatments exist
StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.How: book an appointment for this alone, with a list: flushes, night sweats, sleep, mood, vaginal or urinary symptoms, and changes in bleeding. Ask about hormone therapy, including a patch or gel, and about the non-hormonal options. Why: hormones treat flushes best, and for healthy women under sixty or within ten years of menopause the balance is favorable.
Sources
- 35.Chlebowski, R.T., Anderson, G.L., Aragaki, A.K., Manson, J.E., et al. (2020). "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, 324(4), 369-380. https://doi.org/10.1001/jama.2020.9482 ; Collaborative Group on Hormonal Factors in Breast Cancer (2019). "Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence." The Lancet, 394(10204), 1159-1168. https://doi.org/10.1016/S0140-6736(19)31709-X ; Manson et al. (2017), as above, for cancer mortality. (WHI combined therapy: about 0.45% vs 0.36% a year; the per-1,000 conversion is this book's arithmetic, and the pooled figures assume the association is causal, as the authors state.)
Note numbers are those of Chapter 15, Women's Bodies Across the Life Course.
This verdict is one of the "What you've heard" boxes in Chapter 15, Women's Bodies Across the Life Course, where the book tests the claims people repeat against the studies behind them.
Educational content, not medical advice. Disclaimer.