Objectives: To calculate breast cancer detection to expected incidence ratios and standardised detection ratios (SDRs) for the New Zealand breast cancer screening programme.
Method: Breast cancer registrations for 1976-1999 were obtained from the New Zealand Cancer Registry. Using these registrations, the incidence in the absence of screening was projected for 1999 and 2000. These projections, and the invasive breast cancers detected in the New Zealand programme during 1999 and 2000, were used to calculate the detection to expected incidence ratios and SDRs.
Results: In 1999, the breast cancer detection rate was 5.6 per 1000 women screened. The expected incidence among these women in the absence of screening was 2.3 per 1000, a detection to expected incidence ratio of 2.4. The SDR was 0.84 (0.76-0.94). In 2000, the breast cancer detection rate was 6.0 per 1000 women screened. The expected incidence among these women in the absence of screening was 2.4 per 1000, a detection to expected incidence ratio of 2.5. The SDR was 0.90 (0.81 - 0.99).
Conclusions: In the first two years of the national programme, detection to expected incidence ratios were less than 3.0, and the SDR results were below 1.0. It may be unrealistic to expect new screening programmes to achieve SDRs of 1.0 immediately. At a similar stage, the UK National Health Service Breast Cancer Screening Programme (NHSBSP) also reported SDRs of less than 1.0 and therefore lower than expected cancer detection rates compared with the Swedish Two-County trial. An encouraging finding was that SDRs in five of the six screening regions improved in the second year of the New Zealand screening programme.
