Estrogen Plus Progestin and Lung Cancer: Follow-up of the Women's Health Initiative Randomized Trial

Introduction In the Women's Health Initiative (WHI) estrogen plus progestin trial, after 5.6 years' intervention and 8 years' median follow-up, more women died from lung cancer in the hormone therapy group (hazard ratio [HR], 1.71; 95% confidence interval [CI], 1.16-2.52; P =.01). Now after 14 years' median follow-up, we reexamined combined hormone therapy effects on lung cancer mortality. Patients and Methods In the WHI placebo-controlled trial, 16,608 postmenopausal women aged 50 to 79 years and with an intact uterus were randomly assigned to once-daily 0.625 mg conjugated equine estrogen plus 2.5 mg medroxyprogesterone acetate (n = 8506) or placebo (n = 8102). Incidence and mortality rates for lung cancer were assessed from multivariant proportional hazard models. Results After 14 years' cumulative follow-up, there were 219 lung cancers (0.19% per year) in the estrogen plus progestin group and 184 (0.17%) in the placebo group (HR, 1.12; 95% CI, 0.92-1.37; P =.24). While there were more deaths from lung cancer with combined hormone therapy (153 [0.13%] vs. 132 [0.12%], respectively), the difference was not statistically significant (HR, 1.09; 95% CI, 0.87-1.38; P =.45). The statistically significant increase in deaths from lung cancer observed during intervention in women assigned to estrogen plus progestin was attenuated after discontinuation of study pills (linear trend over time, P =.042). Conclusion The increased risk of death from lung cancer observed during estrogen plus progestin use was attenuated after discontinuation of combined hormone therapy.