Menarche, menopause and breast cancer risk. The lancet oncology, Nov. 2012, Vol. 13(11), p.1071-72.
Britt, K.
http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(12)70456-4/fulltext?rss=yes
The longer a woman is exposed to cycling reproductive hormones the higher her risk of breast cancer. If she has an early menarche or a late menopause, or both, her risk of breast cancer is increased. Additionally, women who bear children (parous) have a decreased risk of breast cancer compared those without children (nulliparous),purportedly because of the break in reproductive cycling. An understanding of how these reproductive behaviours mediate breast cancer risk will help to establish whether the cumulative length of cycling itself increases breast cancer risk, or whether exposure to the mitogenic effects of oestrogen is more important.
