The Women's Health Initiative (WHI) trial changed the landscape of menopausal hormone therapy (MHT). The combined oestrogen-progestogen arm was stopped early in 2002. What was the relative risk of breast cancer found, and what follow-up data from the same trial subsequently modified this interpretation?
- A RR 1.26 for breast cancer; follow-up showed risk persisted after stopping MHT for 10+ years
- B RR 1.38 for breast cancer; follow-up showed risk disappeared within 2 years of stopping MHT
- C RR 1.24 for breast cancer; subsequent analysis showed risk was confined to women who were 'prior hormone users' at baseline, not new initiators ✓
- D RR 1.04 (not significant) for breast cancer in the oestrogen-progestogen arm
Explanation
The WHI oestrogen-progestogen trial (conjugated equine oestrogen + medroxyprogesterone acetate) reported a hazard ratio of 1.26 (95% CI 1.00–1.59) for invasive breast cancer — marginally above 1.0 and nominally significant. Later post-hoc analyses (Chlebowski et al.) showed the increased risk was predominantly in women who had used hormones BEFORE the trial (prior users); women who were hormone-naive at randomisation had no statistically significant increase in breast cancer risk. This nuanced re-analysis, along with differences from the oestrogen-only arm (where risk was REDUCED, HR 0.79), significantly modified clinical recommendations. Current guidance (BMS 2020, NICE 2015 updated) recognises that the breast cancer risk of MHT is modest, context-dependent, and lower than that of alcohol or obesity.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
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Written and medically reviewed by the StethoPrep medical team.