The Gail Model: A Simple Explanation
The Gail Model is a computerized calculator that estimates a woman's risk of developing invasive breast cancer over the next 5 years and over her lifetime, using seven specific risk factors: current age, age at first menstrual period, age at first live birth (or if she never had children), number of first-degree relatives with breast cancer, number of previous breast biopsies, whether any biopsy showed atypical hyperplasia, and race. 1
How the Model Works
The Gail Model produces two key numbers:
- 5-year risk: The probability of developing invasive breast cancer within the next 5 years 1
- Lifetime risk: The probability of developing breast cancer by age 90 1
The model is available as a free online tool at the National Cancer Institute website (http://www.cancer.gov/bcrisktool/Default.aspx) and takes only minutes to complete. 1
Risk Threshold for Clinical Action
A 5-year risk of ≥1.7% is considered "high risk" and was the threshold used to determine eligibility for breast cancer prevention trials with tamoxifen. 1, 2 This 1.7% threshold represents the average risk of a 60-year-old woman, which is the median age of breast cancer diagnosis in the United States. 1
For women aged 35 or older with a 5-year risk ≥1.7%, clinical breast exams every 6-12 months and annual mammography are recommended. 1
Critical Limitations: When NOT to Use the Gail Model
The Gail Model should NOT be used for women under 50 with a strong family history of breast cancer. 1 Specifically, it is inappropriate for:
- Women with known BRCA1/2, TP53, or PTEN gene mutations 1
- Women with a strong family history of breast or ovarian cancer 1
- Women with lobular carcinoma in situ (LCIS) 1
- Women who received chest radiation before age 30 (such as for Hodgkin lymphoma) 1
For women with strong family history, alternative models such as BRCAPRO, BOADICEA, or Tyrer-Cuzick should be used instead, as these models better account for multiple affected relatives and hereditary patterns. 1
Performance Characteristics
The model accurately predicts the number of breast cancer cases in groups of women but has modest discriminatory accuracy for individual women (concordance statistic 0.58). 3 This means while it works well for population-level predictions, it is less precise for determining an individual woman's exact risk ranking. 1, 3
The Gail Model systematically underestimates risk in women with atypical hyperplasia, making them appear ineligible for risk reduction therapy when they may actually benefit. 1 In these cases, the Tyrer-Cuzick model is more appropriate. 1
The model has been updated to provide more accurate risk estimates for African American women (using data from the Women's Contraceptive and Reproductive Experiences study) and for Asian and Pacific Islander women (using data from the Asian American Breast Cancer Study). 1 However, it may overestimate risk for recent immigrants from Japan or China. 1
Clinical Context for Your Patient
For a woman under 50 with a strong family history of breast cancer, the Gail Model is the wrong tool to use. 1 Strong family history requires assessment with family history-based models (BRCAPRO, BOADICEA, Tyrer-Cuzick) that can identify women with >20% lifetime risk who need enhanced surveillance including annual MRI starting at age 25-30. 1 These women may also need genetic counseling and testing for BRCA mutations. 1, 2