title: Effect of changing breast cancer incidence rates on the calibration of the Gail model.
abstract: OBJECTIVE
  The Gail model combines relative risks (RRs) for five breast cancer risk factors with age-specific breast cancer incidence rates and competing mortality rates from the Surveillance, Epidemiology, and End Results (SEER) program from 1983 to 1987 to predict risk of invasive breast cancer over a given time period. Motivated by changes in breast cancer incidence during the 1990s, we evaluated the model's calibration in two recent cohorts.
  
  
  METHODS
  We included white, postmenopausal women from the National Institutes of Health (NIH) -AARP Diet and Health Study (NIH-AARP, 1995 to 2003), and the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO, 1993 to 2006). Calibration was assessed by comparing the number of breast cancers expected from the Gail model with that observed. We then evaluated calibration by using an updated model that combined Gail model RRs with 1995 to 2003 SEER invasive breast cancer incidence rates.
  
  
  RESULTS
  Overall, the Gail model significantly underpredicted the number of invasive breast cancers in NIH-AARP, with an expected-to-observed ratio of 0.87 (95% CI, 0.85 to 0.89), and in PLCO, with an expected-to-observed ratio of 0.86 (95% CI, 0.82 to 0.90). The updated model was well-calibrated overall, with an expected-to-observed ratio of 1.03 (95% CI, 1.00 to 1.05) in NIH-AARP and an expected-to-observed ratio of 1.01 (95% CI: 0.97 to 1.06) in PLCO. Of women age 50 to 55 years at baseline, 13% to 14% had a projected Gail model 5-year risk lower than the recommended threshold of 1.66% for use of tamoxifen or raloxifene but >or= 1.66% when using the updated model. The Gail model was well calibrated in PLCO when the prediction period was restricted to 2003 to 2006.
  
  
  CONCLUSIONS
  This study highlights that model calibration is important to ensure the usefulness of risk prediction models for clinical decision making.
authors.affiliation: Biostatistics Branch, Division of Cancer Epidemiology and Genetics, 6120 Executive Blvd, Bethesda, MD 20892, USA. pfeiffer@mail.nih.gov
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Schonfeld
authors.forename: David
authors.initials: D
authors.lastname: Pee
authors.forename: Robert T
authors.initials: RT
authors.lastname: Greenlee
authors.forename: Patricia
authors.initials: P
authors.lastname: Hartge
authors.forename: James V
authors.initials: JV
authors.lastname: Lacey
authors.forename: Yikyung
authors.initials: Y
authors.lastname: Park
authors.forename: Arthur
authors.initials: A
authors.lastname: Schatzkin
authors.forename: Kala
authors.initials: K
authors.lastname: Visvanathan
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Pfeiffer
mesh_terms: D017677:Age Distribution; D000367:Age Factors; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology / Q000628:therapy; D002138:Calibration; D003661:Decision Support Techniques; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D015233:Models, Statistical; D009361:Neoplasm Invasiveness; D018579:Patient Selection; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D018426:SEER Program; D013997:Time Factors; D014481:United States / Q000453:epidemiology