title: Validation of the Gail model for predicting individual breast cancer risk in a prospective nationwide study of 28,104 Singapore women.
abstract: BACKGROUND
  The Gail model (GM) is a risk-assessment model used in individual estimation of the absolute risk of invasive breast cancer, and has been applied to both clinical counselling and breast cancer prevention studies. Although the GM has been validated in several Western studies, its applicability outside North America and Europe remains uncertain. The Singapore Breast Cancer Screening Project (SBCSP) is a nation-wide prospective trial of screening mammography conducted between Oct 1994 and Feb 1997, and is the only such trial conducted outside North America and Europe to date. With the long-term outcomes from this study, we sought to evaluate the performance of GM in prediction of individual breast cancer risk in a Asian developed country.
  
  
  METHODS
  The study population consisted of 28,104 women aged 50 to 64 years who participated in the SBSCP and did not have breast cancer detected during screening. The national cancer registry was used to identify incident cases of breast cancer. To evaluate the performance of the GM, we compared the expected number of invasive breast cancer cases predicted by the model to the actual number of cases observed within 5-year and 10-year follow-up. Pearson's Chi-square test was used to test the goodness of fit between the expected and observed cases of invasive breast cancers.
  
  
  RESULTS
  The ratio of expected to observed number of invasive breast cancer cases within 5 years from screening was 2.51 (95% confidence interval 2.14 - 2.96). The GM over-estimated breast cancer risk across all age groups, with the discrepancy being highest among older women aged 60 - 64 years (E/O = 3.53, 95% CI = 2.57-4.85). The model also over-estimated risk for the upper 80% of women with highest predicted risk. The overall E/O ratio for the 10-year predicted breast cancer risk was 1.85 (1.68-2.04).
  
  
  CONCLUSIONS
  The GM over-predicts the risk of invasive breast cancer in the setting of a developed Asian country as demonstrated in a large prospective trial, with the largest difference seen in older women aged between 60 and 64 years old. The reason for the discrepancy is likely to be multifactorial, including a truly lower prevalence of breast cancer, as well as lower mammographic screening prevalence locally.
authors.affiliation: Department of Medical Oncology, National Cancer Centre Singapore, 11 Hospital Drive, Singapore 169610, Republic of Singapore.
authors.forename: Wen Yee
authors.initials: WY
authors.lastname: Chay
authors.forename: Whee Sze
authors.initials: WS
authors.lastname: Ong
authors.forename: Puay Hoon
authors.initials: PH
authors.lastname: Tan
authors.forename: Nicholas Qi
authors.initials: NQ
authors.lastname: Jie Leo
authors.forename: Gay Hui
authors.initials: GH
authors.lastname: Ho
authors.forename: Chia Siong
authors.initials: CS
authors.lastname: Wong
authors.forename: Kee Seng
authors.initials: KS
authors.lastname: Chia
authors.forename: Khuan Yew
authors.initials: KY
authors.lastname: Chow
authors.forename: Minhan
authors.initials: M
authors.lastname: Tan
authors.forename: Peter
authors.initials: P
authors.lastname: Ang
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology*; D018270:Carcinoma, Ductal, Breast / Q000000981:diagnostic imaging / Q000453:epidemiology*; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000000981:diagnostic imaging / Q000453:epidemiology*; D015331:Cohort Studies; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography; D008403:Mass Screening; D008875:Middle Aged; D008954:Models, Biological; D012306:Risk; D018570:Risk Assessment; D012846:Singapore / Q000453:epidemiology