The completeness of the Swedish Cancer Register - a sample survey for year 1998

Introduction. The Swedish Cancer Register (SCR) is used extensively for monitoring cancer incidence and survival and for research purposes. Completeness and reliability of cancer registration are thus of great importance for all types of use of the cancer register. The aim of the study was to estimate the overall coverage of malignant cancer cases in 1998 and to reveal possible reasons behind non-reporting. Methods. We selected all malignant cancer cases in the Hospital Discharge Register (HDR) from 1998 and compared these records to those reported to the SCR. There were 43 761 discharges for 42 010 individuals of whom 3 429 individuals were not recorded in the SCR. From these 3 429 records we randomly selected 202 patients for review of their medical records to determine whether they should have been registered on the SCR as incident cases in 1998. Results. About half of the 202 cases (93 malignant and 8 benign) should have been reported, which translates into an additional 1 579 malignant cases (95% CI 1 349-1 808), or 3.7% of the cases reported in 1998. The crude incidence rate for males and females combined would increase from 493 per 100 000 to 511 (95% CI 508-514) if these cases were taken into account. Conclusion. The overall completeness of the SCR is high and comparable to other high quality registers in Northern Europe. For most uses in epidemiological or public health surveillance, the underreporting will be without major impact. However, for specific research questions our findings have implications, as the degree of underreporting is site specific, increases with age, and does not seem to be random, as diagnoses without histology or cytology verification are overrepresented. An annual comparison of the SCR against the HDR could point to hospitals, geographic areas or specific diagnoses where organizational and administrative changes should be introduced to improve reporting.