The concept that breast cancer may be preventable is supported by the wide international variation in breast cancer rates, which is an indicator that there are potentially modifiable environmental and lifestyle determinants of breast cancer. After a transient increase in risk after childbirth, there is a long-term reduction in risk. The degree of risk reduction appears to be related to age. In addition to age at menopause and childbirth, age at menarche is a third factor that has been linked to breast cancer risk. While modulation of reproductive risk factors or hormonal interventions that simulate the preventive effects of early pregnancy or early menopause are theoretically possible, these types of interventions may not be effective for all women, particularly those with a family history of breast cancer.
Breast feeding is associated with a decreased risk of breast cancer.
This observation suggests that women's desires to share information about their history of abortion may be influenced by their social environment, which may, therefore, have a large impact on any observed health outcome that is postulated as being a consequence of abortion. The underlying susceptibility of an individual also influences the degree to which mutagens and growth factors accelerate the carcinogenic process. Deleterious mutations in BRCA2 have been associated with an increased risk of other cancers such as pancreatic cancer and lymphoma. The variations in estimates of risk are due to differences in study populations and mutations evaluated. A case report of identical twins who carry a deleterious BRCA1 mutation in which only one of the twins has developed breast and ovarian cancer emphasizes our lack of knowledge about other factors that influence when and if a deleterious- mutation carrier develops cancer.