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.
Level 2 - randomized trial
Long-term follow-up of two randomized controlled trials
PubMed 32721007 · doi:10.1001/jama.2020.9482
What was done
Long-term follow-up through December 2017 of two randomized, placebo-controlled clinical trials from the Women's Health Initiative involving 27,347 postmenopausal women aged 50 to 79 years across 40 US centers. In women with a uterus (n = 16,608), participants were randomized to 0.625 mg/d conjugated equine estrogen (CEE) plus 2.5 mg/d medroxyprogesterone acetate (MPA) or placebo (median intervention 5.6 years). In women with prior hysterectomy (n = 10,739), participants were randomized to 0.625 mg/d CEE alone or placebo (median intervention 7.2 years). The primary outcome was breast cancer incidence; secondary outcomes included deaths from breast cancer.
What was found
After >20 years median cumulative follow-up (>98% mortality ascertainment): - CEE alone vs placebo (hysterectomized women): significantly lower breast cancer incidence (238 cases [0.30%/year] vs 296 cases [0.37%/year]; HR, 0.78; 95% CI, 0.65-0.93; P = .005) and significantly lower breast cancer mortality (30 deaths [0.031%/year] vs 46 deaths [0.046%/year]; HR, 0.60; 95% CI, 0.37-0.97; P = .04). - CEE plus MPA vs placebo (women with intact uterus): significantly higher breast cancer incidence (584 cases [0.45%/year] vs 447 cases [0.36%/year]; HR, 1.28; 95% CI, 1.13-1.45; P < .001) but no significant difference in breast cancer mortality (71 deaths [0.045%/year] vs 53 deaths [0.035%/year]; HR, 1.35; 95% CI, 0.94-1.95; P = .11).
Why it matters
These long-term findings demonstrate persistent, opposing associations between different menopausal hormone therapy formulations and breast cancer, confirming that CEE alone reduces long-term breast cancer risk and mortality in women with prior hysterectomy, whereas adding MPA increases breast cancer incidence.
Limits
The trials tested only one specific formulation and dose (oral CEE 0.625 mg/d with or without oral MPA 2.5 mg/d), so findings may not generalize to other estrogen types, progestogens (such as micronized progesterone), transdermal routes, or lower doses. The active intervention periods were terminated early (at 5.6 and 7.2 years), and post-trial hormone use or lifestyle changes during the post-intervention observation phase are not described in the abstract.
Cited by
- supports At 19-year follow-up of the Women's Health Initiative CEE plus MPA trial, there remains no significant difference in breast cancer mortality compared to placebo.
- supports In the Women's Health Initiative trial, the CEE alone arm in women without a uterus had a lower incidence of breast cancer and lower breast cancer mortality compared to placebo.