title: Risk factor modification and projections of absolute breast cancer risk.
abstract: BACKGROUND
  Although modifiable risk factors have been included in previous models that estimate or project breast cancer risk, there remains a need to estimate the effects of changes in modifiable risk factors on the absolute risk of breast cancer.
  
  
  METHODS
  Using data from a case-control study of women in Italy (2569 case patients and 2588 control subjects studied from June 1, 1991, to April 1, 1994) and incidence and mortality data from the Florence Registries, we developed a model to predict the absolute risk of breast cancer that included five non-modifiable risk factors (reproductive characteristics, education, occupational activity, family history, and biopsy history) and three modifiable risk factors (alcohol consumption, leisure physical activity, and body mass index). The model was validated using independent data, and the percent risk reduction was calculated in high-risk subgroups identified by use of the Lorenz curve.
  
  
  RESULTS
  The model was reasonably well calibrated (ratio of expected to observed cancers = 1.10, 95% confidence interval [CI] = 0.96 to 1.26), but the discriminatory accuracy was modest. The absolute risk reduction from exposure modifications was nearly proportional to the risk before modifying the risk factors and increased with age and risk projection time span. Mean 20-year reductions in absolute risk among women aged 65 years were 1.6% (95% CI = 0.9% to 2.3%) in the entire population, 3.2% (95% CI = 1.8% to 4.8%) among women with a positive family history of breast cancer, and 4.1% (95% CI = 2.5% to 6.8%) among women who accounted for the highest 10% of the total population risk, as determined from the Lorenz curve.
  
  
  CONCLUSIONS
  These data give perspective on the potential reductions in absolute breast cancer risk from preventative strategies based on lifestyle changes. Our methods are also useful for calculating sample sizes required for trials to test lifestyle interventions.
authors.affiliation: Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 6120 Executive Plaza South, EPS 8049, Bethesda, MD 20892-7244, USA. elisabetta.petracci@gmail.com
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Petracci
authors.forename: Adriano
authors.initials: A
authors.lastname: Decarli
authors.forename: Catherine
authors.initials: C
authors.lastname: Schairer
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Pfeiffer
authors.forename: David
authors.initials: D
authors.lastname: Pee
authors.forename: Giovanna
authors.initials: G
authors.lastname: Masala
authors.forename: Domenico
authors.initials: D
authors.lastname: Palli
authors.forename: Mitchell H
authors.initials: MH
authors.lastname: Gail
mesh_terms: D000328:Adult; D000368:Aged; D000428:Alcohol Drinking; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control*; D016022:Case-Control Studies; D015444:Exercise; D005260:Female; D005544:Forecasting; D006801:Humans; D015994:Incidence; D007558:Italy / Q000453:epidemiology; D007899:Leisure Activities; D008432:Mathematical Computing; D008875:Middle Aged; D015233:Models, Statistical; D012042:Registries; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D040242:Risk Reduction Behavior