ABSTRACT
Breast cancer is the leading cause of cancer death for women 15 to 29 years of age with approximately 11,000 new cases of in situ or invasive breast cancer and 1100 breast cancer deaths in women younger than age 40. While the occurrence of breast cancer at the time of pregnancy or lactation is 3% or less of all women who develop breast cancer, the prevalence increases to over 15% among women before age 40. Epidemiologic studies confirm that pregnancy has a dual effect on breast cancer risk. Childbearing reduces the lifetime risk of developing breast cancer, although risk increases during the time surrounding pregnancy. Women who have their first full-term pregnancy at an early age have a decreased lifetime risk of developing breast cancer. The relationship between age at first full-term pregnancy and risk of breast cancer is likely related to physiologic and hormonal changes that occur during and after pregnancy.
