Breast cancer is the most common cancer in females in the United States and the second most common cause of cancer death in women. Approximately one-half of newly diagnosed breast cancers can be explained by known risk factors, such as age at menarche, first live birth, menopause, and proliferative breast disease. An additional 10% are associated with a positive family history. Risk factors for breast cancer may be modified by demographic, lifestyle, and environmental factors. 
So, what increases our risk? What can we change? What do have no control over? 
Age:  the risk of breast cancer increases with older age.  In recent surveillance risk stratifies as such: Birth to age 39 – 1 in 203 women;  Age 40 to 59 – 1 in 27 women;  Age 60 to 69 – 1 in 28 women; Age 70 and older – 1 in 15 women;  Birth to death – 1 in 8 women.
 
Female gender:  Breast cancer occurs 100 times more frequently in women than in men.  In the United States, over 200,000 women are diagnosed with invasive breast cancer each year, compared with approximately 2000 cases that occur annually in men. 
 
Caucasian race:  the highest rate of breast cancer occurs among white women, although breast cancer remains the most common cancer among women of every major ethnic group.  
 
Weight:  Obesity (defined body mass index ≥30 kg/m2) is associated with an overall increase in morbidity and mortality.  However, the risk of breast cancer associated with BMI appears to depend on the menopausal status of women. 
 
Postmenopausal women:  A higher body mass index (BMI) and/or perimenopausal weight gain have been consistently associated with a higher risk of breast cancer among postmenopausal women.  The association for risk can be explained by higher estrogen levels resulting from the adipose tissue to estrogen.  
 
Premenopausal women:  Unlike postmenopausal women, an increased BMI is associated with a lower risk of breast cancer in premenopausal women.  The explanation of this finding remains unclear.
 
Tall stature:  Increased height is associated with a higher risk of breast cancer in both premenopausal and postmenopausal women.  The mechanism underlying this association is unknown, but may reflect the influence of nutritional exposures during childhood and puberty. 
 
Estrogen levels:  High endogenous estrogen levels increase the risk of breast cancer (particularly hormone receptor-positive breast cancer) in both postmenopausal and premenopausal women. For postmenopausal women, the correlation between an increased risk for breast cancer and increasing hormone levels (eg, estradiol, estrone) has been consistent.  
 
Benign breast disease:  A wide spectrum of pathologic entities is included in the category of benign breast disease. Among these, proliferative lesions (especially those with histologic atypia) are associated with an increased risk of breast cancer. 
 
Dense breast tissue:  The density of breast tissue reflects the relative amount of glandular and connective tissue (parenchyma) to adipose tissue. Breast density is a measure of the extent of radiodense fibroglandular tissue. Women with mammographically dense breast tissue, generally defined as dense tissue comprising ≥75 percent of the breast, have a 4 to 5 times risk of breast cancer compared with women of similar age with less or no dense tissue.  It is unclear whether screening recommendations should differ for women with dense breasts in the absence of other risk factors. 
 
Bone mineral density:  Because bone contains estrogen receptors and is highly sensitive to circulating estrogen levels, bone mineral density (BMD) is considered a surrogate marker for long-term exposure to endogenous and exogenous estrogen. In multiple studies, women with higher bone density have a higher breast cancer risk.
 
Androgens:  Elevated androgen (ie, testosterone) levels have been associated with an increased risk of postmenopausal and premenopausal breast cancer. 
 
Insulin pathway and related hormones: %C