Clinical Edge

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Estrogen-alone Therapy & Invasive Breast Cancer

Menopause; ePub 2018 May 7; Shufelt, et al

Invasive breast cancer risk did not differ significantly in women with a hysterectomy using estrogen-alone therapy when directly comparing different doses, formulations, and routes of delivery to the conventional oral conjugated equine estrogen (CEE), a recent study found. Researchers used data from the Women’s Health Initiative (WHI) observational study. Analyses included 26,525 postmenopausal women with a hysterectomy aged 50-79 years at study entry. They found:

  • Average follow-up was 8.2 years.
  • For CEE users, no difference was observed between low-dose CEE vs conventional-dose CEE for breast cancer (HR, 0.99).
  • Compared with conventional-dose CEE, transdermal estrogen was associated with a nonsignificant lower risk of invasive breast cancer (HR, 0.75).


Shufelt C, Bairey Merz CN, Pettinger MB, et al. Estrogen-alone therapy and invasive breast cancer incidence by dose, formulation, and route of delivery: Findings from the WHI observational study. [Published online ahead of print May 7, 2018]. Menopause. doi:10.1097/GME.0000000000001115.