Andrew Coldman1, Norm Phillips1, Christine Wilson1, Kathleen Decker1, Anna M Chiarelli1, Jacques Brisson1, Bin Zhang1, Jennifer Payne1, Gregory Doyle1, Rukshanda Ahmad1. 1. Cancer Surveillance and Outcomes (AC, NP) and Screening Mammography Program of BC (CW), BC Cancer Agency, Vancouver, British Columbia; Screening Programs, Cancer Care Manitoba, Winnipeg, Manitoba (KD); Ontario Breast Screening Program, Cancer Care Ontario, Toronto, Ontario (AMC); Québec Breast Cancer Screening Program, Institut National de Santé Publique du Québec, Quebec City, Quebec (JB); New Brunswick Breast Cancer Screening Services Program, Fredericton, New Brunswick (BZ); Nova Scotia Breast Screening Program, Halifax, Nova Scotia (JP); Newfoundland and Labrador Breast Screening Program, Eastern Health, St. John's, Newfoundland (GD); Public Health Agency of Canada, Ottawa, Ontario (RA).
Abstract
BACKGROUND: Screening with mammography has been shown by randomized controlled trials to reduce breast cancer mortality in women aged 40 to 74 years. Estimates from observational studies following screening implementation in different countries have produced varyied findings. We report findings for seven Canadian breast screening programs. METHODS: Canadian breast screening programs were invited to participate in a study aimed at comparing breast cancer mortality in participants and nonparticipants. Seven of 12 programs, representing 85% of the Canadian population, participated in the study. Data were obtained from the screening programs and corresponding cancer registries on screening mammograms and breast cancer diagnoses and deaths for the period between 1990 and 2009. Standardized mortality ratios were calculated comparing observed mortality in participants to that expected based upon nonparticipant rates. A substudy using data from British Columbia women aged 35 to 44 years was conducted to assess the potential effect of self-selection participation bias. All statistical tests were two-sided. RESULTS: Data were obtained on 2796472 screening participants. The average breast cancer mortality among participants was 40% (95% confidence interval [CI] = 33% to 48%) lower than expected, with a range across provinces of 27% to 59%. Age at entry into screening did not greatly affect the magnitude of the average reduction in mortality, which varied between 35% and 44% overall. The substudy found no evidence that self-selection biased the reported mortality results, although the confidence intervals of this assessment were wide. CONCLUSION: Participation in mammography screening programs in Canada was associated with substantially reduced breast cancer mortality.
BACKGROUND: Screening with mammography has been shown by randomized controlled trials to reduce breast cancer mortality in women aged 40 to 74 years. Estimates from observational studies following screening implementation in different countries have produced varyied findings. We report findings for seven Canadian breast screening programs. METHODS: Canadian breast screening programs were invited to participate in a study aimed at comparing breast cancer mortality in participants and nonparticipants. Seven of 12 programs, representing 85% of the Canadian population, participated in the study. Data were obtained from the screening programs and corresponding cancer registries on screening mammograms and breast cancer diagnoses and deaths for the period between 1990 and 2009. Standardized mortality ratios were calculated comparing observed mortality in participants to that expected based upon nonparticipant rates. A substudy using data from British Columbiawomen aged 35 to 44 years was conducted to assess the potential effect of self-selection participation bias. All statistical tests were two-sided. RESULTS: Data were obtained on 2796472 screening participants. The average breast cancer mortality among participants was 40% (95% confidence interval [CI] = 33% to 48%) lower than expected, with a range across provinces of 27% to 59%. Age at entry into screening did not greatly affect the magnitude of the average reduction in mortality, which varied between 35% and 44% overall. The substudy found no evidence that self-selection biased the reported mortality results, although the confidence intervals of this assessment were wide. CONCLUSION: Participation in mammography screening programs in Canada was associated with substantially reduced breast cancer mortality.
Authors: J Gagnon; E Lévesque; F Borduas; J Chiquette; C Diorio; N Duchesne; M Dumais; L Eloy; W Foulkes; N Gervais; L Lalonde; B L'Espérance; S Meterissian; L Provencher; J Richard; C Savard; I Trop; N Wong; B M Knoppers; J Simard Journal: Curr Oncol Date: 2016-12-21 Impact factor: 3.677