Objective-The Ontario breast screening program (OBSP) is a provincial breast screening programme oVering 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. (J Med Screen 1998;5:73-80)
The population-based Ontario Breast Screening Program (OBSP) provides two-yearly screening by both nurse examiner clinical breast examination (CBE) and two-view mammography to women aged 50 to 69. CBE alone accounts for about 5% of cancer detection. The purpose of this study was to determine whether CBE information affects radiologists' interpretation of mammography. Interpretation was defined by 1) radiologists' referral rates for diagnostic evaluation and 2) radiologists' accuracy in distinguishing cancer from non-cancer on mammograms. Mammograms were obtained from women randomly selected from those screened in the OBSP between 1990 and 1992. Selection was stratified by whether or not the nurse examiner had independently referred for diagnostic evaluation. Additional women diagnosed with breast cancer were selected to increase the precision of the receiver-operating characteristic (ROC) curve. Each participating OBSP radiologist read a set of mammograms twice, approximately three weeks apart. The first reading was based on mammograms alone. At the second reading, the CBE report was included on the reporting form. Among 620 women referred by the nurse, radiologist referral rate increased from 37.7% to 40.8% (p = 0.079) when CBE information was available. Among the 637 not referred by the nurse, radiologist referral rate decreased from 29.8% to 25.6% (p = 0.005). There was little effect on the sensitivity and specificity of radiologist referral and the areas under the two ROC curves (with and without CBE information) were not significantly different (p = 0.571). Although there was some effect of CBE information on radiologists' pattern of referral, there was no effect on accuracy of cancer detection.
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