Ten years of breast screening in the Screening Mammography Program of British Columbia, 1988-97

Objectives-To evaluate 10 year outcomes of the Screening Mammography Progra m of British Columbia (SMPBC) and determine if breast screening targets wer e being achieved among women aged 40-80+ years. Setting--Organised breast screening programme in British Columbia, Canada. Methods-Rates of participation, abnormal referral, cancer detection, and in terval cancer were calculated for asymptomatic women receiving an SMPBC mam mography from 1988-97. Results-895 839 screening mammographies were provided to 335 433 women. 51. 3% of women were age 50-69 years. Abnormalities were identified on 57 454 s creens (6.4%) from which 3304 cancers were detected. Abnormal call rates we re higher on first (9.8%), compared with subsequent screens (4.4%) and decl ined with age: 7.7% at age < 40 to 5.4% for age 70-79 years. Cancer detecti on rates were higher on first (5.0 per 1000) compared with subsequent scree ns (2.8 per 1000) and increased smoothly with age from 1.4 to 8.2 per 1000 from age < 40 to age 80 years and older. Twenty per cent of cancers were no n-invasive. The median size of invasive cancers was 14 mm and 81% had no ax illary lymph node metastases. The 12 month interval cancer rate was 0.6 per 1000 and did not vary significantly with age or screening history. The pre valence to expected incidence ratio was 3.1 for women age 50-79 years. Conclusion-Across a broad range of ages, surrogate indices of screening mam mography success have been achieved in a population based, North American, organised breast cancer screening programme.