Monitoring the performance of New Zealand's National Cervical Screening Programme through data linkage

To describe the method developed by the National Cervical Screening Programme (NCSP) for review of cases of cervical cancer; present results from the first 4 years of the review and compare these results with those of the earlier New Zealand Cervical Cancer Audit.

Linkage of cervical cancer registrations from the New Zealand Cancer Registry to smear histories from the NCSP Register via the National Health Index, for the 4-year period 2003-06.

A total of 625 women were registered with cervical cancer from 2003-06, of whom 438 were eligible for linkage (women diagnosed with squamous or adenosquamous cervical cancer at <80 years of age). Of these 438 eligible cases, 348 were histologically invasive and 90 were microinvasive. Unlike histological stage, clinical FIGO stage was missing in approximately 50%. Linkage to screening history revealed that 202 of the 438 eligible women (46%) had never been enrolled in the NCSP; 137 (31%) were enrolled but had only been infrequently or irregularly screened; and 85 (20%) developed cancer despite regular screening (data were missing for 3 women). These results were similar to those found in the New Zealand Cervical Cancer Audit, covering the period 2000-2002.

Ongoing linkage of cancer data to screening data can be used to monitor the performance of the NCSP. Our finding that 80% of potentially preventable cervical cancers involve women who are not enrolled in the Programme or who have been only infrequently and irregularly screened, confirms that improving Programme coverage (currently around 72%) remains a priority. Further investigation (phase 2) is required for the small number of women who develop cervical cancer despite regular screening (average of 21 per year, or approximately 20% of eligible cases), to distinguish interval cancers from possible Programme quality issues.