A wide variety of factors may influence an individual's likelihood of developing breast cancer; these factors are referred to as risk factors. The established risk factors for breast cancer include: female gender, age, previous breast cancer, benign breast disease, hereditary factors (family history of breast cancer), early age at menarche (first menstrual period), late age at menopause, late age at first full-term pregnancy, obesity, low physical activity, use of postmenopausal hormone replacement therapy, use of oral contraceptives, exposure to low-dose ionizing radiation in midlife and exposure to high-dose ionizing radiation early in life.
Correlated risk factors for breast cancer include never having been pregnant, having only one pregnancy rather than many, not breast feeding after pregnancy, diethylstilbestrol (DES), certain dietary practices (high intake of fat and low intakes of fiber, fruits, and vegetables), tobacco, smoking, breast trauma, large breast size, synthetic estrogens, electromagnetic fields, and alcohol consumption. Alcohol is known to increase estrogen levels. Alcohol use appears to be more strongly associated with risk of lobular carcinomas and hormone receptor-positive tumors than it is with other types of breast cancer (Li et al. 2003).
A novel growth inhibitor recently identified as estrogen down-regulated gene 1 (EDG1) was found to be switched off (down-regulated) by estrogens. Inhibiting EDG1 expression in breast cells resulted in increased breast cell growth, whereas over-expression of EDG1 protein in breast cells resulted in decreased cell growth and decreased anchorage-independent growth, supporting the role of EDG1 in breast cancer (Wittmann et al. 2003).