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Results from the Ontario breast screening program, 1990–1995

Objective The Ontario breast screening program (OBSP) is a provincial breast screening programme offering two view mammography, clinical breast examination, instruction in breast self examination, and systematic two year recall to Ontario women 50 years and older. This paper presents the results of the programme's intermediate outcomes from 1990 to 1995 and compares them with recommended standards and other published programmes. Methods Programme data from a provincial screening programme in a large Canadian province were collated from 18 sites in operation between July 1990 and December 1995. Results In its first five years of operation, 215 738 screens were performed on 142 173 women. The referral rates for initial and rescreens are 13.8% and 8.6% respectively. A total of 1718 women were diagnosed with cancer, 1325 at initial screens and 393 at rescreens, resulting in cancer detection rates of 9.3 and 5.3/1000. The cancer detection rates for invasive cancers were 8.3/1000 at initial screens and 4.5/1000 at rescreens. The benign to malignant biopsy ratio was 1.5:1 at initial screens and 1.3:1 at rescreens. Of the 1358 cancers diagnosed at initial screens, 11.6% were in situ and 50.3% of invasive cancers of known size were <15 mm. For women with invasive cancer where nodal status was known, 71.3% were node negative. The proportions at rescreens were 15.7%, 60.0%, and 76.0% respectively. Conclusions While the OBSP has achieved the standards suggested by other studies and programmes during its first five years of operation, there is work to be done to increase participation and obtain more complete data on tumour size and nodal status.