Breast Cancer Risk Calculations: The Gail Model
The Gail Model is a statistical breast cancer risk assessment algorithm which was developed by Dr. Mitchell Gail and his colleagues with the Biostatistics Branch of NCI’s Division of Cancer Epidemiology and Genetics. It was developed following a huge screening study of 280 000 women between 35 and 74 years of age. The Gail model has shown to be a reasonable tool for estimating breast cancer risk in white women, and other researchers have subsequently supplemented the model to provide accurate risk assessments for African American, Hispanic, and Asian women.
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Basic variables of the Gail Breast Cancer risk assessment model
The Gail model looked at a women’s personal medical history, familial history, and reproductive history. Specifically it considered the number of previous biopsies and the presence of any kind of atypical hyperplasia on any of them. It also took into account the age of start of menstruation and age at first live birth of a child, and also the incidence of breast cancer among first degree female relatives. These variables were then adjusted according to increasing age brackets and associated higher risk for older women. The Gail model did not take into account racial or ethnic differences, BRCA genetic variants, tamoxifen use, and excluded women who had already had a confirmed diagnosis of either ductal or lobular breast carcinoma in situ. And according to some researchers, there is an indication that the Gail model underestimates the risk of breast cancer development in women with pre-existent atypical breast hyperplasia.
The risk assessment tool has subsequently been modified by the University of Texas Southwestern Medical Center at Dallas, the National Surgical Adjuvant Breast and Bowel Project, and other researchers in Canada and Europe. (Breast Cancer risk calculator).
Other breast cancer risk modifiers in recent assessment models
New breast cancer risk calculators now take into account other known risk factors such as alcohol consumption, use of birth control pills, dense breast tissue, the prior incidence of DCIS and LCIS, and also racial characteristics. (African American, Asian, and Hispanic women are shown to be at higher risk). Tamoxifen is also considered a risk modifier; it tends to lower risk but only for women for whom it has been prescribed due to age and other histological findings (such as the presence of LCIS or BRCA variants). Other new models take into account dietary habits and lifestyle, but the effect of ‘modifiable‘ variables (excluding hormone therapies) on a genetically predisposed disease like breast cancer is generally over-estimated.
Some other risk factors are not usually included in risk modelling because they are known ‘high risk‘ factors. These include the presence of BRCA1 and BRCA2 genetic variants, and hormonal increases resulting from post-menopausal hormone therapies. However, it should be noted that the ‘risk effects‘ associated with hormone replacement therapy are really not consistent enough to be accurately modeled at this time.
Below are a couple Q&A about The Gail Model.
- What are the 7 key risk factors for breast cancer? age, age at first period, age at the time of the birth of her first child (or has not given birth at all), family history of breast cancer (mother, sister, or daughter), number of past breast biopsies, number of breast biopsies showing atypical hyperplasia, and race/ethnicity.
- What is the individual risk vs. the group risk? The breast cancer risk assessment tool cannot predict whether or not you will develop breast cancer. It does not calculate an individual woman’s breast cancer risk. Instead, it gives the average risk for a group of women with similar risk factors. So, it is not clear what this risk means for any one woman. Say the tool gives you a five-year risk of 1%. This means that the tool estimates that 1% of women who have risk factors similar to yours will develop breast cancer over the next five years. But, the tool cannot predict which of these omen will get breast cancer.
- How can you interpret your estimated risk? The breast cancer risk assessment tool (The Gail Model) was designed to be used by health care providers. So, if you use the tool on your own, it may be hard to understand what the risk it calculates means for you. If you have any questions about your risk of breast cancer, talk to your provider.
- What are some limitations of The Gail Model? This breast cancer risk assessment tool does not give a good estimate of risk in some women including those with a personal history of invasive breast cancer, DCIS, or LCIS. Or a strong family history of breast cancer, who may have an inherited gene mutation. It is still not clear how well the model works in other ethnic groups. The Gail Model also does not use all the known risk factors for breast cancer to assess risk. Even with it’s current limitations, this breast cancer risk assessment tool can be very useful. However, it is not a perfect predictor of individual risk. The model can estimate your risk, but it cannot tell whether or not you will get breast cancer.
- Gail MH, Brinton LA, Byar DP, Corle DK, Green SB, Shairer C, Mulvihill JJ: Projecting individualized probabilities of developing breast cancer for white females who are being examined annually. J Natl Cancer Inst 81(24):1879-86, 1989.
- Rockhill B, Spiegelman D, Byrne C, Hunter DJ, Colditz GA: Validation of the Gail et al. model of breast cancer risk prediction and implications for chemoprevention. J Natl Cancer Inst 93(5):358-66, 2001.
- National Surgical Adjuvant Breast and Bowel Project. http://www.nsabp.pitt.edu
- University of Texas Southwestern Medical Center at Dallas. http://www.utsouthwestern.edu/
- Halls.md Breast Cancer Risk Calculator. http://www.halls.md/breast/risk.htm
- Decarli, A., Calza, S., Masala, G., Specchia, C., Palli, D., Gail, M.H. Gail Model for Prediction of Absolute Risk of Invasive Breast Cancer: Independent Evaluation in the FlorenceEuropean Prospective Investigation Into Cancer and Nutrition Cohort. Journal of the National Cancer Institute 2006 98(23):1686-1693
- Boyle P, Mezzetti M, La Vecchia C, Franceschi S, Decarli A, Robertson C. Contribution of three components to individual cancer risk predicting breast cancer risk in Italy. Eur J Cancer Prev 2004;13:18391
- Palomares MR, Machia JR, Lehman CD, Daling JR, McTiernan A.Mammographic density correlation with Gail model breast cancer risk estimates and component risk factors. Cancer Epidemiol Biomarkers Prev. 2006 Jul;15(7):1324-30.
- Bernatsky S, Ramsey-Goldman R, Boivin JF, Joseph L, Moore AD, Rajan R, Clarke A.Do traditional Gail model risk factors account for increased breast cancer in women with lupus?J Rheumatol. 2003 Jul;30(7):1505-7.
- Elmore JG, Fletcher SW. The risk of cancer risk prediction: "What is my risk of getting breast cancer"? J Natl Cancer Inst. 2006 Dec 6;98(23):1673-5.
- Pankratz VS, Hartmann LC, Degnim AC, Vierkant RA, Ghosh K, Vachon CM, Frost MH, Maloney SD, Reynolds C, Boughey JC.Assessment of the accuracy of the Gail model in women with atypical hyperplasia.J Clin Oncol. 2008 Nov 20;26(33):5374-9.
- Cummings SR, Tice JA, Bauer S, Browner WS, Cuzick J, Ziv E, Vogel V, Shepherd J, Vachon C, Smith-Bindman R, Kerlikowske K.Prevention of breast cancer in postmenopausal women: approaches to estimating and reducing risk.J Natl Cancer Inst. 2009 Mar 18;101(6):384-98.