The most proven and significant risk factors are being female and getting older.

In other words, all women are at risk for breast cancer with the greatest risk occurring after the age of 55 years. There are many other known endogenous (i.e., related to one's individual body) and exogenous (i.e., related to lifetime exposures, including toxins, environmental changes, and medicines) risk factors for female breast cancer.

Hormonal Factors

The major breast cancer risk factors are "hormonal" and related to a woman's reproductive history. The greatest risk results from long periods of uninterrupted menstrual or ovulatory cycles. In these situations, breast tissue is consistently exposed to estrogen. Hormonal factors that increase risk include:

• The birth of a first child after the age of 30 or not having children at all
• Menstruation starting at an early age (before 12)
• Late menopause (after 55)
• Although debated, many experts say taking birth control pills and/or hormone replacement therapy slightly increases one's risk

Genetic Factors

Over the past decade, two breast cancer usceptibility genes have been discovered and characterized, BRCA-1 and BRCA-2. Certain mutations (changes) in either of these genes will increase a woman's risk of breast cancer. Those with a well-documented genetically inherited predisposition to breast cancer only account for about 5-10% of cases diagnosed. These women have a higher risk of developing breast cancer at a younger age (before menopause), and they often have multiple family members with the disease.

• A woman may be a higher risk if she has a close relative who has had breast cancer before menopause or in both breasts.
• There is up to 10 times greater risk if one's mother or sister had cancer in both breasts. There is a 6 times greater risk if one's mother or sister had breast cancer prior to menopause.

Environmental and Lifestyle Factors

There are several known environmental and lifestyle risk factors including:

• More than mild or moderate alcohol consumption. Alcohol may raise levels of estrogen in the blood.
• Obesity with excess caloric and fat intake. Like alcohol, fatty tissue is thought to raise estrogen levels.
• More than moderate meat intake. Studies have shown an 18% difference in risk of breast cancer between those with highest and those with lowest levels of meat intakes. Meat may raise estrogen levels and be a potential source of mutagens.
• Country of origin (the frequency of breast cancer varies about 5 fold between countries although migrants from low risk countries like Japan and China to high risk countries like Canada and the US eventually acquire the risk of their adopted country).
• High levels of radiation to the chest (not from mammogram).

Personal history

• A personal history of breast or ovarian cancer.
• A previous breast biopsy showing abnormal cells.

Source for risk factors: Understanding Breast Cancer Risk by Andrew Joe, MD; New York Presbyterian Medical Center