What measurable risk factors are associated with breast cancer?

According to the NCI's Breast Cancer Risk Assessment Tool, these include:

A personal history of breast abnormalities. A history of lobular or ductal carcinoma in situ is associated with an increased risk of invasive breast cancer. ("In situ," which means "confined in that site," here describes types of breast cancer in which cancer cells stay within your breast's lobules - milk factories, so to speak - or within the ducts that carry the milk to the nipple.)

Breast cancer among first-degree relatives. Your risk rises if your mother, sisters, and/or daughters have had the disease.

Age at first period and first live birth. If menstruation began before you were 12, if you had your first child after you were 30, or never had children, you're at increased risk.

Breast biopsies. A history of breast biopsy increases risk (not from the biopsy itself, but from whatever prompted it). Risk is raised further if results showed what's known as "atypical hyperplasia," or a benign, but abnormal increase in the number of normal cells.

Your age. Most breast cancers develop in women older than 50.

Race. White women are at increased risk, although a higher percentage of black women with breast cancer die from it.

Are there other possible risk factors?

Yes, several other factors were excluded from the currently available risk assessment formulas because the evidence so far is inconclusive or researchers have been unable to measure their contribution to overall risk. These are age at menopause, alcohol use, dense breast tissue, use of birth control pills or hormone replacement therapy, high-fat diet, radiation exposure, and environmental pollutants.
I've heard there are now drugs I can take to prevent getting breast cancer.

Do they work and are they safe?

If your answers to questions on the "risk disk" put you into the high-risk category, discuss with your obstetrician-gynecologist the risks versus benefits of taking tamoxifen for you as an individual. In 1998, because of impressive findings about tamoxifen from the Breast Cancer Prevention Trial (BCPT), the FDA approved the use of this drug "to reduce the incidence of breast cancer in women at high risk." Tamoxifen has its drawbacks, however - among them, a greater risk for uterine cancer - and it is not for everyone. Other, possibly safer drugs, such as raloxifene (Evista), are being studied. You might ask your doctor about participating in the NCI's 5-year clinical trial called STAR (Study of Tamoxifen and Raloxifene), which will compare the two drugs.

What about genetic testing?