title: Comparing screening mammography for early breast cancer detection in Vermont and Norway.
abstract: BACKGROUND
  Most screening mammography in the United States differs from that in countries with formal screening programs by having a shorter screening interval and interpretation by a single reader vs independent double reading. We examined how these differences affect early detection of breast cancer by comparing performance measures and histopathologic outcomes in women undergoing opportunistic screening in Vermont and organized screening in Norway.
  
  
  METHODS
  We evaluated recall, screen detection, and interval cancer rates and prognostic tumor characteristics for women aged 50-69 years who underwent screening mammography in Vermont (n = 45 050) and in Norway (n = 194 430) from 1997 through 2003. Rates were directly adjusted for age by weighting the rates within 5-year age intervals to reflect the age distribution in the combined data and were compared using two-sided Z tests.
  
  
  RESULTS
  The age-adjusted recall rate was 9.8% in Vermont and 2.7% in Norway (P < .001). The age-adjusted screen detection rate per 1000 woman-years after 2 years of follow-up was 2.77 in Vermont and 2.57 in Norway (P = .12), whereas the interval cancer rate per 1000 woman-years was 1.24 and 0.86, respectively (P < .001). Larger proportions of invasive interval cancers in Vermont than in Norway were 15 mm or smaller (55.9% vs 38.2%, P < .001) and had no lymph node involvement (67.5% vs 57%, P = .01). The prognostic characteristics of all invasive cancers (screen-detected and interval cancer) were similar in Vermont and Norway.
  
  
  CONCLUSIONS
  Screening mammography detected cancer at about the same rate and at the same prognostic stage in Norway and Vermont, with a statistically significantly lower recall rate in Norway. The interval cancer rate was higher in Vermont than in Norway, but tumors that were diagnosed in the Vermont women tended to be at an earlier stage than those diagnosed in the Norwegian women.
authors.affiliation: Department of Screening-Based Research, The Cancer Registry of Norway, Oslo, Norway.
authors.forename: Solveig
authors.initials: S
authors.lastname: Hofvind
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Vacek
authors.forename: Joan
authors.initials: J
authors.lastname: Skelly
authors.forename: Donald L
authors.initials: DL
authors.lastname: Weaver
authors.forename: Berta M
authors.initials: BM
authors.lastname: Geller
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000473:pathology / Q000517:prevention & control; D018270:Carcinoma, Ductal, Breast / Q000000981:diagnostic imaging / Q000453:epidemiology; D042241:Early Diagnosis; D004522:Educational Status; D005260:Female; D006801:Humans; D008327:Mammography / Q000592:standards / Q000706:statistics & numerical data*; D008403:Mass Screening / Q000379:methods / Q000458:organization & administration / Q000592:standards / Q000706:statistics & numerical data*; D008875:Middle Aged; D009367:Neoplasm Staging; D009664:Norway / Q000453:epidemiology; D015588:Observer Variation; D011379:Prognosis; D014707:Vermont / Q000453:epidemiology