One in 8 women will develop breast cancer over the course of a lifetime. But that doesn't mean all of us are at equal risk of being "the one." Your physician uses a statistical model to determine where you fall on the probability scale.
At some point during your annual physical, the doctor will bring up your risk of breast cancer. If s/he doesn't - bring it up yourself, or find a new doctor; breast cancer is the second most common cancer in women (after lung cancer). And while you shouldn't fear it, you should have breast cancer on your health radar.
Just as you understand your risk of heart disease, stroke, diabetes, and other possibly life-threatening conditions, you need to know how likely you are to be diagnosed with breast cancer, based on two factors: heredity (genetics), and lifestyle. Why? In order to make breast health a priority, via noticing breast changes, and having regular screening mammograms (once age-appropriate).
So, exactly how does your doctor go beyond "1 in 8" to determine your own personal risk of breast cancer at any point in time?
S/he uses one or more types of risk models, carefully constructed guidelines based on years of data around the many elements that factor into a breast cancer diagnosis.
BRCA1/2 models are used to determine whether or not a woman may be carrying certain gene mutations that can increase her lifetime risk of breast cancer from the American national average of about 12% to over 80%.
This model, of which there are numerous types, uses information about the patient's ethnicity, family history of breast and ovarian cancer, and the patient's own cancer history to determine whether genetic testing would be desirable.
If the answers indicate a possibility the patient is carrying the BRCA1/2 mutations, her doctor may recommend genetic testing, which can then prove or disprove the model's prediction.
Overall, these BRCA risk models successfully predict about 50% of the women who aren't at genetically increased risk for breast cancer. About 10% of the time, the model misses women who will eventually be identified as carrying damaged BRCA genes.
Another type of model your physician can use predicts your absolute risk of developing breast cancer during a specific time period (e.g., between ages 40-50). This takes the "1 woman in 8" average to a more time-specific, personal level.
Why is the age-specific component important? Because it helps your doctor (and you) decide your breast cancer screening strategy. Do you need to start having regular mammograms before age 40? Do you need one every year, or can you go 2 to 3 years in between?
Developed in 1989, the original GAIL model is based on a long-term study of over 283,000 women from around the U.S., which began in 1973 and concluded in 1980, with follow-up studies continuing through 1998. Sponsored by the American Cancer Society and National Cancer Institute, the study assessed a number of lifestyle-based risk factors, including use of hormone replacement therapy, diet, body weight, exercise, and occupation.
GAIL 2 model
A revision of the first model, GAIL 2 adds information about first-degree family members diagnosed with breast cancer. GAIL 2 is what your doctor currently uses to predict your risk of invasive breast cancer. A high score on GAIL 2 determines a healthy woman's eligibility for breast cancer prevention drugs (e.g., tamoxifen); and also identifies women appropriate for inclusion in breast cancer prevention clinical trials.
The model isn't without its shortcomings. It's most accurate for non-Hispanic white women receiving annual mammograms, since that's the population on which the initial study was based. However, it's the most accurate model currently available, and as such forms the basis for the
National Cancer Institute Breast Cancer Risk Assessment Tool, a "quick and dirty" tool doctors use to begin the breast cancer conversation with their patients.
Since neither GAIL nor GAIL2 proved effective enough for determining breast cancer risk in black women, a third model was developed using data from the 2006-2013 Women's Contraceptive and Reproductive Experiences (CARE) study. Unlike the study on which the original GAIL model was based, CARE included a significant number of black women. The CARE model has proven its validity, and has been incorporated into the NCI's Breast Cancer Risk Assessment Tool.
Want to check your own breast cancer risk? Use the NCI's Breast Cancer Risk Assessment Tool. Discuss results with your doctor before using them to inform your choices around screening and prevention.
Breast cancer risk assessment tool. (2011, May 16). Retrieved from http://www.cancer.gov/bcrisktool/
http://clinicaltrials.gov/ct2/show/nct00341159. (2013, September). Retrieved from http://clinicaltrials.gov/ct2/show/NCT00341159
Schairer, C. (2013, March 22). The breast cancer detection demonstration project (BCDDP) follow-up study . Retrieved from http://epi.grants.cancer.gov/Consortia/members/bcddp.html
Stopeck, A. (2013, August 19). Breast cancer risk assessment models. Retrieved from http://emedicine.medscape.com/article/1945957-overview?src=wnl_edit_specol&uac=158026HG