[Relation of breast cancer tumour stage and the degree of registration in a population-based cancer registry].
Population-based cancer registries provide a large database of cancer cases which can be used for evaluation of cancer epidemiological and care-related questions. In particular, the latest projects in breast cancer screening and quality assured breast cancer diagnostics represent appropriate databases in the use of cancer registry data for further evaluation. For breast cancer the tumour stage distribution is a well suited, early available indicator for evaluating such interventions. The problem in using data from cancer registries occurs with the rather long time period until registration can be completed (up to 3 years). Thus, early usage of cancer registry data remains rather questionable.


OBJECTIVE
This analysis aims to show whether the distribution of breast cancer tumour stage depends on the completeness of registration and whether a valid estimate of the tumour stage distribution is possible at an early stage, on the basis of a not fully completed registration.


METHODS
The cancer registry records all new cancer cases of the Federal State of Schleswig-Holstein. For the period from 1998 to the beginning of 2003 all breast cancer cases and their tumour stage distribution were extracted at three-month' intervals. Completeness of registration for each date was estimated on the basis of cancer data from the Federal State of Saarland. The expected number of breast cancer cases for Schleswig-Holstein was set to 100%.


RESULTS
In total, 7,418 patients with new breast cancer were analysed. Already at a degree of 50% of registration a stable distribution of tumour stage could be observed. For example, the variability of the T1-category (tumour size < or = 2 cm) showed a maximum of three per cent in the range from 50% up to 100% completeness. Also for lymph nodes and distant metastases just a small degree of variability from one to three per cent points could be shown. A 75% completeness of breast cancer registration was established about six months after the end of the year of diagnosis. Complete registration could only be reached significantly later, approximately after two years.


CONCLUSIONS
For the cancer registry of Schleswig-Holstein a significant relation of the tumour stage distribution in the degree of registration could not be detected. A stable distribution could be shown with a completeness of 50-75%. Hence, it appears to be methodically justified to analyse the tumour stage of breast cancer data with sufficient validity with a completeness of 75 %. The tumour stage distribution can be used as an early indicator (about six months after the end of the year of diagnosis) for evaluation of projects like mammography screening, quality management or research on medical care.
D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000473:pathology / Q000517:prevention & control; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008207:Lymphatic Metastasis; D008403:Mass Screening; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging; D012042:Registries; D013997:Time Factors