Reproductive Health · 2004
Women's Health Initiative: Estrogen-Alone Hormone Therapy
When the estrogen-progestin arm of the Women's Health Initiative was halted in 2002, it left an important question unanswered: was the progestin component responsible for the cardiovascular and breast cancer harm, or did estrogen itself contribute? The WHI's parallel estrogen-alone arm, running separately in the 10,739 hysterectomized women who did not require progestin, was still ongoing and positioned to answer that question directly.
Marcia Stefanick at Stanford led the principal analysis. The arm had enrolled postmenopausal women aged 50 to 79, randomizing them to conjugated equine estrogen at 0.625 mg daily or placebo. The NHLBI stopped the trial in February 2004 after 6.8 years, not because of a single boundary crossing, but on the basis of accumulated evidence across multiple endpoints. Jacques Rossouw oversaw the decision from the NHLBI. The JAMA paper published in April 2004 reported a hazard ratio for coronary heart disease of 0.91, with 95% confidence intervals of 0.75 to 1.12: no significant benefit, and no significant harm from a cardiac standpoint.
Stroke risk, however, was significantly elevated: a hazard ratio of 1.39, translating to roughly 12 additional strokes per 10,000 person-years. That finding aligned with the combination-arm result and indicated that stroke risk was attributable to estrogen itself, not to the progestin. Breast cancer incidence trended lower with estrogen alone, with a hazard ratio of 0.77, a difference that reached statistical significance in extended follow-up analyses published after the main paper.
The contrast between the two WHI arms generated clinical nuance that the original 2002 paper could not provide. Progestin appeared to drive most of the breast cancer excess seen in the combination arm; estrogen alone showed a different profile, with stroke risk elevated but breast cancer risk potentially reduced. Those differences, cautiously interpreted, fed into later discussions about the choice of progestogen type and route of administration in women who do require endometrial protection.
Both WHI arms confirmed the same core conclusion for guideline purposes: hormone therapy of either formulation could not be recommended for primary cardiovascular prevention. Subgroup analyses from the estrogen-alone arm suggested that women initiating therapy within 10 years of menopause had more favorable coronary outcomes than those beginning a decade or more after; that observation shaped the nuanced prescribing framework in current guidelines, which restrict hormone therapy to symptom management in younger postmenopausal women at acceptable risk.
Key People
- Marcia Stefanick — Stanford; principal investigator, WHI estrogen-alone analysis
- Jacques Rossouw — NHLBI project officer; WHI oversight
- JoAnn Manson — Brigham and Women's Hospital; WHI investigator and timing-hypothesis research
JAMA, 2004
Related landmarks
- 2002 · Magpie Trial: Magnesium Sulfate for Pre-eclampsia (Reproductive Health)
- 2002 · Women's Health Initiative: Estrogen plus Progestin Hormone Therapy (Reproductive Health)
- 1997 · Dolly the Cloned Sheep (Reproductive Health)
- 1995 · Collaborative Eclampsia Trial: Magnesium Sulfate for Eclampsia (Reproductive Health)