Breast Cancer Causes
by Beth G. Hodges, MD

Causes of breast cancer or risk factors for same are multiple. The most prominent risk factor for breast cancer is a family history of it. The risk lies with 2 genes, BRCA1 and BRCA2.

Before having genetic testing done, a woman with a family history of breast cancer should get counseling as to what the information does and does not mean. Having one of these genes does not mean a woman will develop breast cancer; it just means she has increased potential to do so. That type of information can be a motivator to early breast cancer screening or encourage a woman to be more compliant with annual mammography and monthly self breast exam, or it can be a dark cloud hanging over a woman's head unnecessarily. Some women have even chosen elective bilateral mastectomies (which is the surgical removal of both breasts) to allay their fears.

Another risk factor for breast cancer is increasing age. Most breast cancers occur after age 60, though some of the more aggressive types often occur earlier.

The type of estrogen in oral contraceptives (aka birth control pills) is not felt to cause breast cancer, but the type of estrogens used in hormone replacement therapy may be associated with a small increase in risk.

Of note, several studies have shown that women who develop breast cancer while on postmenopausal estrogen replacement therapy (ERT)are less likely to die from their cancer than women who are not on ERT at the time of diagnosis. One theory is that something about the ERT keeps the cancer localized to the breast, whereas it is the "spreading out" of the cancer to other parts of the body that worsens the prognosis. Another theory is that women on ERT have to be more on schedule with regular mammograms and annual physicals in order to obtain refills on that ERT, whereas women not on ERT may fall behind on routine visits, leading to later diagnosis.

Other circumstances that lead to increased lifelong exposure to estrogen (even the estrogen found naturally in the body) also leads to increased risk of breast cancer. For example, early onset of menstruation (before age 12), late menopause (after age 55) and not having children or having a first child later in life can increase a woman's overall risk.

Obesity has been associated with increased risk of breast cancer, as has high fat diet. Heavy alcohol use (more than 2 drinks per day) has also been associated with increase in occurrence of breast cancer.

Smoking increases incidence of most types of cancer, but the association in particular with breast cancer is not overly strong. Still, if a woman is concerned about her risk of breast cancer, smoking cessation is certainly prudent.

Published - October, 2009