What is the effect of menstrual and obstetric history breast cancer risk?

Updated: Dec 16, 2019
  • Author: Jessica Katz, MD, PhD, FACP; Chief Editor: Marie Catherine Lee, MD, FACS  more...
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Factors that increase the number of menstrual cycles also increase the risk of breast cancer, probably due to increased endogenous estrogen exposure. Such factors include the following:

  • Menarche when younger than 13 years (2 times the risk)
  • Nulliparity
  • First full pregnancy when older than 30 years
  • Not breastfeeding
  • Menopause when older than 50 years

Conversely, late menarche, anovulation, and early menopause (spontaneous or induced) are protective, owing to their effect on lowering endogenous estrogen levels or shortening the duration of estrogenic exposure.

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