What is the Gail model?
The Gail model is a statistical model used in the US National Cancer Institute's (NCI) Breast Cancer Risk Assessment Tool (BCRAT). It estimates a woman's chance of developing invasive breast cancer within the next 5 years and up to age 90. It was first published in 1989 and has been updated since. This tool uses exactly the same method as the NCI's open-source BCRA package.
What information is used?
- Age: the model applies to women aged 35-85.
- Age at first period: an early first period slightly increases risk.
- Age at first live birth: a first birth after 30, or no births, increases risk.
- First-degree relatives with breast cancer: a mother, sister or daughter with breast cancer.
- Number of breast biopsies and atypical hyperplasia: having had biopsies, and atypical hyperplasia in a biopsy, increase risk.
How is it calculated?
First, separate relative risks are calculated for before and after age 50. The relative risk is combined with breast cancer rates by age observed in US women (SEER data) and the chance of dying from other causes to find the absolute risk for each year of age, and these are added up. The "average woman" shown for comparison is the model's risk for a woman of the same age with no known risk factors.
How to read the result
- 5-year risk: the chance of developing breast cancer in the next 5 years. In the US a value of 1.67% or more is considered "increased risk" and is used as a threshold when discussing options such as preventive medication.
- Lifetime risk: the chance of developing breast cancer by age 90. It is about 12% for an average woman; a risk of around 20% or more may prompt additional screening, although that decision is not based on this model alone.
A low percentage does not mean you will not develop breast cancer, and a high one does not mean you certainly will. The result is helpful background when you discuss screening and follow-up with your doctor.
Limitations
- The model was developed with data from women in the United States and has not been validated for women in Türkiye; the actual risk here may differ. This tool uses the rates the NCI tool applies to white women.
- It is not suitable for women previously diagnosed with breast cancer, DCIS or LCIS, carriers of BRCA1/BRCA2 or another hereditary cancer syndrome, or women who had chest radiotherapy before 30; for them it underestimates risk.
- Cancers on the father's side, second-degree relatives, relatives' age at diagnosis, ovarian cancer history and breast density are not included. Genetic counselling may be more appropriate for women with several relatives who had breast or ovarian cancer.
When to see a doctor
If you notice a breast lump, bloody nipple discharge, an inverted nipple, orange-peel skin or swelling in the armpit, get checked regardless of the result. Women with a family history of breast cancer at a young age or ovarian cancer are also advised to discuss genetic assessment with their doctor. This tool is for information only; your doctor decides on your screening and follow-up plan.
Sources
- Gail MH, Brinton LA, Byar DP et al. Projecting individualized probabilities of developing breast cancer for white females who are being examined annually. J Natl Cancer Inst. 1989;81:1879-1886.
- Costantino JP, Gail MH, Pee D et al. Validation studies for models projecting the risk of invasive and total breast cancer incidence. J Natl Cancer Inst. 1999;91:1541-1548.
- National Cancer Institute. BCRA: Breast Cancer Risk Assessment R package, version 2.1.2 (CRAN).