Mutations in two different genes, called BRCA1 and BRCA2, have been associated with early breast cancer in some families (up to 50% of female family members can be affected). These families are rare and are thought to account for only about 4% of all breast cancer cases. Most inherited breast cancer risks result from the interaction of several mutated genes. Families with this pattern of inheritance will contain only a few members with breast cancer. These mutated genes by themselves are associated with only a small increase in breast cancer risk, but several of these genes if inherited together may lead to a significant increase in breast cancer risk.
Diet and lifestyle may modify inherited breast cancer risk but more scientific work is needed to identify and understand the complex mechanisms.
Many studies have evaluated whether the established risk factors for breast cancer (such as age of menarche, age of menopause, age of first pregnancy) might affect women with a family history of breast cancer differently. Data confirm the assumption that family history preliminarily displays a risk factor itself.




A few studies have examined the correlation of eating habits with breast cancer risk for women with a family history of breast cancer. Postmenopausal women with a family history of breast cancer who used to eat 5 or more servings of fruits and vegetable a day could reduce their breast cancer risk by 71%; no effect was reported for women without a family history (Nurses health study). More recently, a decreased risk associated with carotene rich foods (such as carrots, sweet potatoes and broccoli), breast feeding and strenuous activity during early adulthood was reported.
A large cohort study based in Iowa, USA, found a synergistic correlation between family history and waist-to-hip ratio, the size of the waist divided by the size of the hips. Women with a high waist-to-hip ratio (also called apple shaped) and a family history of breast cancer showed a 3.2-fold increase in breast cancer risk compared to women without this body characteristic or family history. In contrast, women with the same waist to hip ratio but without a family history of breast cancer had little or no increase in breast cancer risk.

The determination of genetic polymorphisms is a new means to study the etiology of polygenetic disorders with complex inheritance patterns, such as breast cancer. Single nucleotide polymorphisms (SNPs) can be responsible for more or less broad variation of phenotypes. The correlation between breast cancer and the genotype of SNPs (e.g. CYP1A1) has been intensively investigated in the past few years. It seems most likely, by now, that a number of SNPs coincides with a lightly but significantly increased risk of sickening from breast cancer. Specific surgical or drug interventions such as prophylactic mastectomy and ophorectomy or prophylactic intake of tamoxifen are not indicated based on SNP analysis at this time.

Also epigenetic changes during development of breast cancer have been detected. New methods like methylation-specific digital karyotyping (MSDK) showed epigenetic alterations in different tissues of normal and cancerous breast tissue. The microenvironment of breast duct cells seems to play a crucial role in breast cancer development.

Environmental factors like obesity, nutrition, physical activity and motility, socio-economic status, exposure to electromagnetic fields and nicotine are correlated with the risk of breast cancer. However, only radioactivity and hormonal factors (estrogen-imitating) are accepted risk factors. Organochlorine pesticides and their metabolites (DDT/DDE, HCB, HCH, pyrethroide, PCP, and PCB) have received the most attention since they are persistent in the environment, accumulate in food chains (premliminarily in adipose tissue), and are, hence, detectable even in breast milk.

For further reading visit:
Program on Breast Cancer and Environmental Risk Factors at The Sprecher Institute for Comparative Cancer Research, Cornell University
Management of Hereditary Breast Cancer: Genetic Epidemiology
Gene Testing of Breast Cancer (BRCA)
Pesticides and Breast Cancer Risk: A Review of DDT, DDE, and Dieldrin by S.M. Snedeker