How does the duration of use of postmenopausal hormones affect a woman's risk for breast cancer?

Updated: Dec 26, 2019
  • Author: Graham A Colditz, MD, DrPH; Chief Editor: Chandandeep Nagi, MD  more...
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In the meta-analyses, significant increases in risk of approximately 30%-45% with more than 5 years of use have been observed. In updated results from the Nurses' Health Study, [43] with 1935 breast cancer cases, an excess risk of breast cancer was limited to women with current or very recent use of postmenopausal hormones. Within this group, the risk increased with longer duration of use and was statistically significant among current users of 5 or more years’ duration (eg, compared to never users of postmenopausal hormones, RR for 10 or more years of use = 1.47; 95% CI, 1.22-1.76). Risk is greater for users of estrogen plus progestin compared to users of estrogen alone. [44]

These epidemiologic results were corroborated by the Women’s Health Initiative (WHI), a randomized controlled trial of estrogen plus progestin use that showed a significant increase in risk of breast cancer with duration of use of this hormone combination. [45] Given the high dropout and noncompliance with therapy during the trial, analysis of compliers showed a substantially greater increase in risk with duration of therapy closer to that observed in epidemiologic studies, which, by their nature, evaluate risk among compliers or users of hormone therapy.

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