Affiliations of authors: Chronic Disease Prevention Division, Centre for Chronic Disease Prevention and Control, Health Canada, Ottawa, Ontario, Canada (JO, CMB); Database Management Committee, Canadian Breast Cancer Screening Initiative, Calgary, Alberta, Canada (CPP).
Correspondence to: Jay Onysko, MA, Chronic Disease Prevention Division, Centre for Chronic Disease Prevention and Control, Health Canada, 120 Colonnade Rd., P.L. 6701B, Ottawa K1A 1B4, Canada (e-mail: jay_onysko{at}hc-sc.gc.ca)
In the article by Elmore et al. (1), the authors conclude that abnormal recall rates in North American screening programs appear to be higher than those in other countries without evident benefit in cancer detection rates. As a representation of screening mammography in North American countries outside the United States, the authors cite findings from 11 824 mammography screening examinations conducted during the first 15 months of a single organized program in British Columbia, Canada, between 1988 and 1989. Since that time, program-based mammography screening has grown in Canada, with published outcome data (as of 19992000) available for 3 476 433 screened women from 10 organized screening programs (25). For Elmore et al. to make inferences regarding the state of mammography screening in "North America" on the basis of their limited data generalizes their findings too broadlythat is, the data by Elmore et al. is too limited in terms of coverage, amount (i.e., data were included from only one in 10 programs from Canada and only seven programs from the United States), and timeliness to be considered representative of current screening practices in North America as a whole.
Indicators of screening program performance provide useful information for program evaluation; however, these indicators should be considered within the context of the screening program as a whole. In addition, inference about differences in program performance requires more comprehensive analysis of quantitative and qualitative differences between programs than those offered by Elmore et al. (1). For example, Elmore et al. do not fully consider that quantitative relationships between abnormal recall rates, positive predictive value, and cancer detection rates alone do not provide a meaningful indication of program performance. Further information about interval cancer detection rates and the underlying breast cancer incidence rates are required for such interpretation. Elmore et al. also do not consider qualitative differences between programs that impact upon the unwanted effects of screening as indicated by low positive predictive values. In Canada, follow-up for the majority of abnormal patient recalls consists of noninvasive procedures. For example, in 19992000, imaging procedures, including diagnostic mammographic examination and/or ultrasound, were the only assessment required for nearly three-quarters of women with a screening abnormality (4). Consequently, the positive predictive value of biopsy performed in Canada presently meets or exceeds both Canadian and international standards (6). Hence, if the comparison by Elmore et al. of positive predictive values of biopsy performed had distinguished between the types of diagnostic assessment, including the type of biopsy performed (i.e., fine-needle aspiration versus core biopsy versus open biopsy), the relative burden of diagnostic assessment may have been more apparent.
International comparisons of mammography screening programs can provide valuable information to aid in optimizing their screening performance when rigorous approaches are applied to contrast and combine results from different countries. The Performance Parameters Evaluation Group of the International Breast Cancer Screening Networka consortium of 25 countriesis systematically assessing the feasibility of making international comparisons of screening program performance (see http://appliedresearch.cancer.gov/ibsn/research/activities.html). Their approach includes the standardization of performance measure definitions, data collection methods, and the formulas for calculating program performance and the consideration of confounding contextual factors, such as the inclusion of clinical breast examination during a screening examination, rates of nonprogram screening in the program's target population, and the completeness of cancer registration. In the absence of such an approach, international comparison of screening program performance deserves cautious interpretation and provides limited information for the refinement of screening program policy.
REFERENCES
1 Elmore JG, Nakano CY, Koepsell TD, Desnick LM, D'Orsi JC, Ransohoff DF. International variation in screening mammography interpretations in community-based programs. J Natl Cancer Inst 2003;95:138493.
2 Paquette D, Snider J, Bouchard F, Olivotto I, Bryant H, Decker K, et al. Performance of screening mammography in organized programs in Canada in 1996. The Database Management Subcommittee to the National Committee for the Canadian Breast Cancer Screening Initiative. CMAJ 2000;163: 11338.
3 Health Canada. Organized breast screening programs in Canada 1997 and 1998 report. Ottawa, Ontario (Canada): Minister of Public Works and Government Services Canada, 2001.
4 Health Canada. Organized breast screening programs in Canada 1999 and 2000 report. Ottawa, Ontario (Canada): Minister of Public Works and Government Services Canada, 2003.
5 Bancej C, Decker K, Chiarelli A, Harrison M, Turner D, Brisson J. Contribution of clinical breast examination to mammography screening in the early detection of breast cancer. J Med Screen 2003;10:1621.[CrossRef][ISI][Medline]
6 Health Canada. Report from the Evaluation Indicators Working Group: guidelines for monitoring breast cancer screening program performance. Ottawa, Ontario (Canada): Minister of Public Works and Government Services Canada, 2002.
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