Journal of the National Cancer Institute Advance Access published online on July 29, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn224
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© The Author 2008. Published by Oxford University Press.
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Comparing Screening Mammography for Early Breast Cancer Detection in Vermont and Norway
Affiliations of authors: Department of Screening-Based Research, The Cancer Registry of Norway, Oslo, Norway (SH); Office of Health Promotion Research (SH, BMG), Department of Medical Biostatistics (PMV, JS), and Department of Pathology (DLW), University of Vermont, Burlington, VT
Correspondence to: Berta M. Geller, EdD, Office of Health Promotion Research, University of Vermont, 1 South Prospect Street, Burlington, VT 05401 (e-mail: berta.geller{at}uvm.edu).
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.
Conclusion: 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.
| CONTEXT AND CAVEATS Prior knowledge Opportunistic screening mammography in Vermont differs from organized screening mammography in Norway in several respects, including the screening interval, which is longer in Norway than in Vermont. These differences make it challenging to compare parameters that are associated with the provision and quality of the screening process (ie, performance measures). Study design An evaluation of 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. Contribution Screening mammography detected cancer at about the same rate and at the same prognostic stage in Norway and Vermont, but with a lower recall rate in Norway. The interval cancer rate was higher in Vermont than in Norway, but the Vermont women with interval cancers were diagnosed with earlier-stage tumors than the Norwegian women. Implications Despite its longer screening interval, the organized population-based screening program in Norway achieved similar outcomes as the opportunistic screening in Vermont. Norwegian women were exposed to half as many screening mammograms and fewer recall examinations than the Vermont women, yet the tumor characteristics for all invasive cancers diagnosed were not different between the two screened populations. Limitations Subtle differences in the Vermont and Norwegian data definitions and collection procedures may have influenced the findings. The effects of differences in screening interval could not be distinguished from those of other potential differences in mammography performance between Vermont and Norway. From the Editors
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Manuscript received February 15, 2008; revised May 13, 2008; accepted June 4, 2008.
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J Natl Cancer Inst 2008 100: 1045.
J Natl Cancer Inst 2008 100: 1045.
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